Biology and Culture of Percid Fishes

The family Percidae exclusively is native to freshwaters of the Northern Hemisphere, with just two of its genera divided between Eurasia and North America. Percidae comprises 11 genera and an estimated 266–275 species, reaching tremendous species richness in the North American darters. We provide an up-to-date account relating the results of the latest DNA sequence and morphological analyses to resolve the relationships of the family Percidae, including its component genera and species. We provide newly assembled distribution maps for the taxa, and summarize their primary distinguishing morphological characters and life history. For each genus, the latest phylogenetic tree of species relationships is shown and explained. We relate these findings to historic biogeography and contemporary distributions. Just recently, tremendous inroads have been made using new molecular tools and analyses that allow us to begin to understand the tremendous evolutionary diversification of the Percidae, as well as the landscape and climate factors that have shaped these patterns. This information may provide an important indication of the future responses of percid taxa to continued anthropogenic influences.

The large percids, including

Perca

and

Sander

species, are economically and ecologically important species that inhabit large temperature regions of the Northern Hemisphere. In this chapter, we provide an overview of the environmental biology of the

Perca

(including yellow perch

P. flavescens

and Eurasian perch

P. fluviatilis

) and

Sander

(including walleye

S. vitreus

, pikeperch

S. lucioperca

, and sauger

S. canadensis

) genera, on which the majority of fisheries and aquaculture practices are focused. Through a comprehensive literature review, we discuss how individual- and population-level vital rates, including growth, foraging, reproduction, recruitment, and mortality, are mediated by biotic (e.g., density dependence, resource availability) and abiotic (e.g., temperature, light) environmental variables. As fisheries exploitation is a major source of size-selective mortality in many percid populations, we also examine the potential impacts of fishing mortality on both population metrics and individual vital rates, and identify several research areas that require further investigation. Through this review we aim to identify the major environmental drivers of variation in percid vital rates and thereby inform management practices for both wild and cultured percid populations.

The annual reproductive cycles of percid fish have been clearly characterized for males and females in various natural habitats mainly from North-America or Eurasia, including morpho-anatomical, histological and physiological studies. From this strong basal knowledge, numerous experimental approaches were conducted to understand the environmental and hormonal controls of these reproductive cycles, and to develop artificial programmes in order to obtain delayed or out-of season spawning. It was demonstrated that photoperiod and temperature variations were the major environmental cues. Now efficient photo-thermal programmes exist and have been used by SMEs in intensive fish farming conditions (water recirculating systems).

Artificial reproduction, being a specific human intervention in the process of reproduction, is a key step in aquaculture of percid fishes. This group of fish, exhibits specific traits, considered amenable to artificial reproductive protocols. For example, this is the only extensively studied group of freshwater teleosts where application of human chorionic gonadotropin (hCG) and gonadoliberine analogues (GnRHa) alone, promotes final oocyte maturation (FOM) and spawning without any other hormonal therapy, whereas in other species (cyprinids, catfishes or salmonids) anti-dopaminergic treatment is also needed. Another characteristic trait is that percid females can release their eggs spontaneously in the tank, regardless of the presence of males. This makes artificial spawning of these fish relatively difficult. In the present chapter endocrine regulation as well as reproductive protocols applied to this group of fish are reviewed extensively, however, the focus of this review is on the final gamete maturation, spermiation and ovulation processes are the steps considered from artificial reproduction perspectives. The published data revealed that scientific activity was focused mainly on the problem of synchronization of ovulation and the effectiveness of different hormonal therapies. This evolved into the development of several specific protocols and methods (e.g. percid-specific pre-ovulatory maturational stages of oocytes), which allowed improvement of that in these species. It was also established, that hCG or GnRHa applied alone are the most effective spawning agents in wild or pond-reared percids. However, there is still a considerable lack of data considering the effectiveness of these protocols in controlled reproduction of domesticated broodstocks. Apart from that, there are many other aspects to be investigated. Such as hormonal regulation of final gamete maturation and spawning, verification of some reproductive protocols as possible gamete quality determinants and gamete management protocols (prior to and following fertilization), which were relatively scarcely studied.

In percids, the spermatozoon is acrosomeless and asymmetrical in shape. The head of the spermatozoon is spherical and contains the genomic material. Mitochondria and proximal and distal centrioles are located in the midpiece of the spermatozoon. The flagellum consists of an axoneme with a “9 + 2” microtubule structure surrounded by a plasma membrane. The length of spermatozoa flagella is between 30 and 35 μm. The volume of sperm and spermatozoa concentration highly differs among species and individuals. Seminal plasma is composed of both mineral and organic compounds and has osmolality about 300 mOsmol kg

−1

to maintain the spermatozoa in the quiescent state. A hypo-osmotic shock is required to trigger initiation of spermatozoa motility after discharge into an aquatic environment. The duration of sperm motility lasts from several seconds to a few minutes, however sperm motility kinetics (percentage of motile spermatozoa, spermatozoa velocity and beating frequency of flagella) rapidly decrease after initiation of sperm motility due to rapid depletion of energy source required for the axonemal beating. The environmental osmolality, pH and ionic concentrations affect sperm motility kinetics. The highest percentage of spermatozoa motility and spermatozoa velocity are observed in an activation medium with osmolality of 100 mOSmol kg

−1

. There are various factors that affect semen quality in male broodfish including photoperiod and seasonal regimes, nutrition and antinutritional factors, rearing condition and age and size of broodfish. For short-term storage, it is essential to dilute semen in an ionic extender (300 mOsmol kg

−1

) with or without antibiotics. Methanol (6–10 %) and dimethyl sulfoxide (10 %) can be used as cryoprotectant for sperm cryopreservation.

For a sustainable breeding process, the optimization of recirculating aquaculture system(s) (RAS) fish rearing conditions and the control of out-of-season reproduction, it is important (i) to define intrinsic and extrinsic factors regulating the fish life cycle and (ii) to have a good knowledge of what makes a good ovum, embryo or larva. In the present chapter, we first describe the current knowledge on ova characteristics and the proper embryonic and larval development progress for several percid species. Indeed, it is important to well define the correct sequence of events in order to better characterize potential impairments. The characterization of ova defects or developmental failures (mortality or abnormalities occurrence) may allow the definition of different categories/levels of quality. This quality scale could help scientists and fish breeders to choose the most relevant quality indicators depending on their technical or scientific problem. Indeed, indicators could be either predictive, to assess ova quality, or studied after fertilization to determine embryonic and/or larval abilities to develop properly and reach key steps in addition to the ova quality. However, the possible indicators allowing precise determination of the egg and larvae quality are actually scarce. Some morphological parameters in most cases allow indicating, with high probability, high (e.g. intensiveness of cortical reaction in pikeperch) or low (e.g. oil droplets fragmentation in ovulated eggs of Eurasian perch and pikeperch) egg quality rather than quantifying the real quality. Moreover, there is still no clear molecular predictors of the egg and larvae quality due to the too few or ambiguous data obtained in the field. On the base of the most recent studies it seems that in many cases molecular analyses are one of the most promising methods possibly allowing an estimation of the ova, embryos and larvae quality. But the research activities in this field are still in progress.

Morphology and arrangement of various receptors in Teleostei indicate trophic and environmental preferences of different species. In the Percidae family, the sensory system begins to develop during embryogenesis and evolves over the larval and juvenile stages. The olfactory placodes develop between 26 (

Gymnocephalus

sp.) and 78 (walleye,

Sander vitreus

) hours post fertilization (hpf). However, the olfactory epithelium becomes fully developed at the age of about 1 month, as in the pikeperch (

Sander lucioperca

). During the ontogeny of fish, taste buds develop later than the olfactory system. In pike-perch juveniles, the first taste buds appear 13 days post hatching, primarily in the mouth and the gills, but later on they become visible in other parts of the body. During embryonic development of percids, the eye is the first sense organ to form.

Gymnocephalus

sp. show well developed eyes already after 26 hpf, while in walleye embryos the optic vesicles are fully formed after 70 hpf. Fish maintain body balance thanks to their inner ear (labyrinth), while the movement and vibration in the surrounding water is detected by canal neuromasts of the lateral line and superficial neuromasts of the skin. In the embryos of different percid species auditory vesicles appear after 26–70 h of development, while the lateral line – after 103 h.

In percid fishes, the development of digestive structures and activities is quite similar to that of other carnivorous species (sea bass and sea bream). In most species at hatching, the digestive tract is a simple tube consisting of undifferentiated cells. The mouth and anus are closed and the esophagus is not connected with the intestine. Liver and pancreas are undifferentiated. Digestive enzymatic activities (pancreas, intestine) are detected shortly after hatching. According to histological and enzymatic studies, important changes occur around mouth opening (fifth to seventh dph). The pancreas shows exocrine activity and the liver becomes functional with adipogenic and glycogenic functions. The primary stomach develops in pikeperch and even earlier in Eurasian perch. Pancreatic (trypsin, amylase) and intestinal (leucine-alanine peptidase, Alkaline phosphatase, aminopeptidase N) enzyme activities increase at mouth opening. Leucine-alanine peptidase (cytosolic enzyme) activity declines after mouth opening concurrently with the strong increase of the brush border membrane enzymes (Alkaline phosphatase, leucine-aminopeptidase N) activity indicating the development of the brush border membrane of intestinal enterocytes. The stomach development occurs between 15th and 20th dph in pikeperch and between 21th and 35th in Eurasian perch. Pepsin activity is detected only on day 29 in pikeperch as well as in Eurasian perch larvae and is concurrent with the development of gastric glands. The development of brush border membrane of the intestinal enterocytes and the gastric activity indicate that larvae acquire an adult mode of digestion. The digestive structures and activities can be affected by the nature and the diet composition. This aspect is also discussed in this chapter allowing an approach of the nutritional requirements of percid larvae.

For carnivorous species producing relatively small larvae, as Eurasian perch and yellow perch, the successful rearing of early life stages is still a matter of concern, even if significant improvements have been achieved during these last two decades. This chapter presents an overview of the different methods used to produce juveniles of these two species: (i) production of fish in fertilized ponds, with fingerling habituation to artificial feed before or after pond harvest, (ii) fertilization of mesocosms and semi-intensive production up to 45 days old, (iii) intensive production in tanks with supply of live prey progressively replaced by artificial feed. For each system, the optimal husbandry conditions as well as the influence of main factors (stocking density, temperature, growth heterogeneity and management of cannibalism, non-inflation of swim bladder,…) influencing the survival and growth of fish from larval to juvenile stages are described.

Throughout the last decade, intensive rearing of pike perch fry have developed from small research based setups to full commercial scale operations with capacities to support the fry requirements of large scale highly intensified recirculating aquaculture system(s) (RAS) for ongrowing of the species. The methodology has to a large extent been transferred from the knowledge and prior research in marine larval rearing, using live feeds and recirculation technology. Specific adaptations to pikeperch have included feeding strategies that takes into account that pikeperch larvae are reared in fresh water, and the fact that pikeperch are highly cannibalistic already at the pre weaning stage.

This chapter describes early life stages and reviews intensive larviculture of Walleye (

Sander vitreus

) from hatch to 35 days posthatch (dph). Embryonic development, egg incubation and chemotherapy for eggs, as well as details of gas bladder inflation and methodology to overcome non-inflation of the gas bladder (NGB) are illustrated with photographs from microvideography and artwork. Husbandry includes description of stocking density, as well as environmental features (light, tank color, turbid water, surface spray, and tank hygiene) needed to overcome the problem of clinging behavior and NGB. Consideration is given to use of live and manufactured feeds as well as feeding rate and frequency. The problem of deformities as well as occurrence and treatment of disease and are given appropriate attention. The chapter demonstrates a science-based, production-scale protocol for Walleye fry culture that can achieve 60–70 % survival from hatch to 35 days post hatch (dph). The chapter supports the viewpoint that intensive larviculture offers a practical alternative to pond-culture for production of feed-trained juvenile Walleyes.

This chapter provides a brief review of the current state of knowledge regarding fish skeletal muscle characteristics, factors affecting muscle growth, and proteomic based research in teleost fish with emphasis on percids. Part of the review includes a study that investigated genetic outcome that underlie the growth potential of muscle of yellow perch

Perca flavescens

. More specifically, it compared skeletal muscle sarcoplasmic proteins/peptides between fast- and slow-growing yellow perch in order to identify the differences in expression of skeletal muscle proteins in fish exhibiting different growth capabilities. Briefly, the study identified bands that presented different staining intensities between fast- and slow-growing fish by using 1D electrophoresis. It also demonstrated muscle metabolic enzymes identified by protein sequencing using nano-LC/MS/MS. The results of the present work contribute to the identification of genetic traits that affect the growth superiority in fish in controlled conditions. Therefore it could become a tool for selection of breeders with the potential for increased protein accretion associated with rapid muscle growth, and hence, the production of larger fish.

In commercial aquaculture, knowledge about and means for predicting growth rates, feed intake and energy requirements of the farmed animal in different conditions is essential for the viability of the enterprise. As percid fish species are relatively new in culture, there are no models available to estimate the energy requirement of the cultured fish, which in turn limits the opportunities to calculate the required daily feed allowance. Classical bioenergy budgets are often used to describe energy intake in relation to different energy expenditures of fish by quantifying steps where energy expenditures occur. However, in commercial aquaculture the objective is to optimize the output (growth) in relation to the energy intake, e.g. where energy expenditures occur is less important. In this chapter, we put together data from the scientific literature to produce an alternative model for prediction of the daily growth and energy need of percid fish in general and Eurasian perch (

Perca fluviatilis

L.) in particular. A practice for calculating the daily feed allowance is presented where local rearing conditions can be taken into account. This makes the model applicable to commercial enterprises and may improve feed management, fish growth and thus economics of the fish farms. This chapter also discusses how factors such as season and culture conditions influence the energy requirements and energy expenditures of the percid fish.

A bioenergetics model for a percid fish represents a quantitative description of the fish’s energy budget. Bioenergetics modeling can be used to identify the important factors determining growth of percids in lakes, rivers, or seas. For example, bioenergetics modeling applied to yellow perch (

Perca flavescens

) in the western and central basins of Lake Erie revealed that the slower growth in the western basin was attributable to limitations in suitably sized prey in western Lake Erie, rather than differences in water temperature between the two basins. Bioenergetics modeling can also be applied to a percid population to estimate the amount of food being annually consumed by the percid population. For example, bioenergetics modeling applied to the walleye (

Sander vitreus

) population in Lake Erie has provided fishery managers valuable insights into changes in the population’s predatory demand over time. In addition, bioenergetics modeling has been used to quantify the effect of the difference in growth between the sexes on contaminant accumulation in walleye. Field and laboratory evaluations of percid bioenergetics model performance have documented a systematic bias, such that the models overestimate consumption at low feeding rates but underestimate consumption at high feeding rates. However, more recent studies have shown that this systematic bias was due, at least in part, to an error in the energy budget balancing algorithm used in the computer software. Future research work is needed to more thoroughly assess the field and laboratory performance of percid bioenergetics models and to quantify differences in activity and standard metabolic rate between the sexes of mature percids.

The behaviour of percid fishes

The behaviour of percids, as in most other fishes, is to a great extent size dependent. As the fish grows larger there is a change in behaviour in accordance with a shift in relative costs and benefits of different alternative actions. While a diet of plankton is the most energy efficient for a small percid, with increasing size, larger, more energy rich food types become accessible and more profitable to eat. In connection with a change in diet, a change in foraging habitat also occurs. However, perch with different body shape has been found to differ in diet and occupy different habitats even within one lake. The perch and the pikeperch are, in general, social species but also group size changes with size. The young fish benefit more by being in a large shoal, as a protection against predators. With growth, the groups of fish become smaller, but still, foraging is more effective in groups than when alone. The behaviour of percids also depends on the environment in which they live. For example, risk-taking behaviour is influenced by lake- and size-specific risk of predation. Even though behaviour may be innate to a certain extent, experience is probably important to form the behaviour patterns of individual fish. For the best result in culture it is very important to have knowledge about the behaviour of percids in the wild, especially regarding feeding and social interactions.

Three different production systems are used for perch ongrowing: (1) traditional extensive polyculture system, (2) semi-intensive culture farming and (3) intensive perch farming under RAS (Recirculating Aquaculture System(s)). Extensive and semi-intensive culture systems have many production limitations. Therefore, intensive perch farming has been developed in Europe for more continuous and predictive marketable perch production.

Marketable perch production under RAS is affected by several main factors of production system. Optimal value and condition of each factor for stable and maximal perch production under RAS are described and recommended in details in this chapter.

Overall, white, grey and black tank walls with light regime 12L:12D or 18 L:8D and light intensity 200–1,100 lx create optimal light conditions for intensive ongrowing perch culture. Freshwater or water with salinity under 4 ‰ with temperature 22–24 °C, oxygen saturation around 60–72 % and very low ammonia (below 0.3 mg N-NH

3

 · L

−1

) and nitrite (below 0.5 mg NO

2

−

 · L

−1

) concentrations are optimal conditions for intensive perch production. Disturbance (cleaning of tanks, fish size-sorting etc.) must be reduced at minimum level for providing of maximal production which is the highest under optimal fish biomass from 10 to 20 kg · m

−3

for 10 g perch to 60–70 kg · m

−3

for 150 g perch under RAS.

Cultural technology is described for on-growing Walleye (

Sander vitreus

) on formulated feeds from pond- and tank-reared fingerlings to sub-adult. Current literature is reviewed and a description given of the regimen used by the Iowa Department of Natural Resources, Rathbun Fish Hatchery (RFH) for production of Walleye fingerlings for enhancement stocking. At that site, the production interval is 155 days from hatch to fall fingerling with three phases: (I) pond-culture, (II) habituation to formulated feed indoors, (III) on growing outdoors to 250 mm (140 g). For many years, the critical limitation was during phase II, but academic and applied research on feed composition, tank environment, and fingerling size now allows 85–90 % survival during habituation of pond fingerlings to formulated feeds. In phase III, use of grading fish before stocking has reduced cannibalism and a practical protocol for treatment of common diseases has increased survival. Considerations for post-stocking survival have included improvement in methods for harvest and transport. Suggestions are given for future research to further improve growth and survival, and strategies are for discussed for application of the RFH protocol to produce fish for the food-fish market.

Since the 1980s, angler interest in recreational fisheries has increased the demand for pond production of North American and European percids for stocking to enhance wild populations or to establish new populations. In this paper, we analyze the fish and plankton ecology in the production ponds to provide a better understanding of the ecological and biological factors involved in optimal pond production of percid fingerlings for stocking. Much of the literature uses a “black-box method” for optimizing pond management, reporting on the survival, growth, and size at harvest of fish from ponds as a function of various fertilization and pond stocking regimens. In contrast, our research since 1987 has focused on the seasonal variation in the ecological interactions among fertilizers, algae, zooplankton, benthos, and larval fish in ponds. Accordingly, in this paper we examine management of large-scale production of percid fingerlings from an ecological perspective, concentrating primarily on our research through 2012 in three Ohio state fish hatcheries, incorporating other information from the literature as appropriate. We find that despite differences in walleye, saugeye, and yellow perch growth and development, rearing ponds can be managed similarly to produce desired size and harvest yields of fingerling fish by providing adequate food resources. Management protocol for fertilization, stocking schedules, and stocking density should be site specific considering the source water quality. Further, sequential culture of ponds may boost overall hatchery production, but we show reduced springtime percid yield due to carryover effects of chemicals added during summertime catfish culture.

The factors responsible for the lifetime growth patterns of percids in natural populations can provide meaningful insights for culture operations. Here, we present a summary of a number of well-studied factors and review the current state of knowledge. We illustrate an informative approach to describe lifetime growth of percid species by applying a biphasic growth model to European perch and pikeperch populations, and discuss life-history constraints considering biphasic growth. An evaluation of proposed hypotheses for proximate mechanisms of female-biased sexual size dimorphism in percids is presented, indicating that reduced feeding in males is the most parsimonious explanation given the current evidence. Growth rates in percids are strongly temperature-dependent, and show strong evidence of countergradient growth. Percids also show significant density-dependent growth, demonstrating twofold variation in individual growth rates. Predation, food availability and prey particle size can also affect the efficiency of percid growth. Parasitism and disease in percids are not as well studied as other factors reviewed here within an ecological context, but the reported effects on percid growth vary from negative to neutral to positive. Our review of drivers of natural variation in percid growth will assist culture operators with regards to broodstock selection, husbandry and maintenance of cultured percids.

Up to date, the nutritional requirements of breeders and early life stages of European percid fishes,

Perca fluviatilis

and

Sander lucioperca

, have not been defined precisely, and, in fish farms, breeders are still relying on the regular supply of forage fish. It has been demonstrated in both species that the feeding conditions of broodstock largely influence the quality of gametes (especially in females) and hatched larvae. The best results, in terms of hatching rate and survival to challenge tests during the first days post-hatching, have been obtained when breeders were fed on forage fish, either as unique feed source or in combination with dry feed. Experimental diets, based on a suitable supply of phospholipids (PLs) and adequate ratio of essential long chain fatty acids (docosahexaenoic, eicosapentaenoic and arachidonic acids) have been used successfully in Eurasian perch breeders to produce high quality eggs and larvae, comparable to those obtained from perch fed forage fish. Fatty acid composition of broodstock diet significantly influenced the fatty acid composition of eggs. On the other contrary, none of the characteristics of the sperm were significantly modified by the HUFAs ratio, neither in terms of sperm volume and density, spermatozoa motility and velocity, nor in terms of seminal plasma osmolality. During the first weeks of larval rearing,

Artemia

nauplii are still currently used as starter feed for both Eurasian perch and pikeperch larvae. Enrichment of nauplii with HUFA has proved to be efficient in pikeperch but not in Eurasian perch. At the end of feeding trials with pikeperch larvae, highly significant correlations were achieved between dietary ascorbic acid content and the ascorbic acid content in larval carcass or the reduction of larval deformity. Based on commercial larval feed formulated for marine or freshwater fish, it has been shown that the freshwater feed (containing low Ca/P ratio) was more suitable for pikeperch larvae and juveniles than marine fish diet, in terms of growth, survival and resistance to stress test. Recently, some experimental dry diets varying by their phospholipid content have been tested. The highest survival and growth rates of pikeperch post-larvae (first fed with

Artemia

nauplii) were obtained in groups fed 9.5 % of PLs but higher levels still need to be tested, eventually at an earlier stage of development.

We reviewed the current state of knowledge regarding the function of lipids and fatty acids in teleost reproduction with an emphasis on freshwater fish. Along with this review, we also provide readers with a specific case study on the effect of dietary lipids characterized by different fatty acid profiles on the reproduction of yellow perch. The unique nature of this case study stems from the use of a natural diet (fish) to feed the yellow perch broodstock over a period of two spawning seasons while monitoring reproductive efficiency and offspring viability. Furthermore, we were able to characterize the fatty acid profiles of the neutral and phospholipid fraction of egg lipid. We demonstrate significant decreases in the polyunsaturated fatty acids in gonad lipids of both, the neutral and the phospholipid fractions, an effect that was exacerbated during the second spawning season. The yellow perch however, demonstrated considerable resilience in protecting essential fatty acid concentrations in the gonads and no significant effects on offspring viability were found. As a result of this research we propose a unique pathway for the synthesis, deposition and mobilization of wax esters in yellow perch ovaries and eggs/embryos that requires further study and provides a new approach to diet formulation for larval stages of this species.

In the context of inland aquaculture diversification in Europe, some percid fishes, namely Eurasian perch and pikeperch, are receiving increasing attention from scientists and fish farmers. Significant improvement in the knowledge of percid fish feeding and nutrition during their ongrowing stage has been achieved during these last two decades. The relative importance of different abiotic and biotic factors on feeding activity of percid fishes was investigated. Among them, water temperature, feeding frequency, photoperiod and fish density were identified as factors of prime importance. Rearing European percid fishes at a high density in relatively warm water (22–27 °C) and fed three meals per day with a day length of up to 12 h a day significantly improve fish feeding activity, and, in the same way, the growth performances. Optimization of growth performances under artificial conditions was also investigated through the characterization of their nutritional requirements in terms of protein, lipid and carbohydrate. Depending on the fish life stage, artificial diets containing 43–50 % protein, 13–18 % lipid and 10–15 % carbohydrate cover the nutrient requirements of percid fishes and support the highest growth performance. Moreover, recent advances in the use of alternative oil sources in percid nutrition suggest a high potential of these species to biosynthesize HUFA when fish oil is replaced by plant oil rich in PUFA. In this context of fish ingredients replacement by plant sources, it could be of high interest to investigate the possibility of replacing fish meal by plant products in the future.

Percid fish displayed a labile sexual development and a sexual growth dimorphism towards females that could be used to improve the productivity under controlled conditions. This chapter reviews the different methods that could be used to control the development of the phenotypic sex in order to produce all-female populations for the improvement of growth in Percid fish culture. Techniques of hormonal sex reversal treatment and chromosomes set manipulation (triploidisation and gynogenesis) are described and compared within the different Percid species.

Interspecific hybrids of several percids have been produced, and some of their production characteristics have been compared with purebreds. Most hybrids exhibited superior growth and survival when compared with same egg-source purebreds, however hybrids derived from parental stocks that produced smaller eggs displayed poorer survival (hybrid yellow perch) and similar growth (hybrid sauger) when compared to the purebred parental stocks that produced larger eggs (Eurasian perch and walleye, respectively). Hybrid walleye and sauger have been shown to be reproductively competent. Performance differences of walleye and sauger hybrids derived from varying geographic stocks were noted and may be a source of future production gains. The use of percid hybrids in aquaculture may be limited by regulatory concerns over the importation and introduction of alien invasive species.

The yellow perch

Perca flavescens

and the walleye

Sander vitreus

are native North American percid fishes, which have considerable fishery and ecological importance across their wide geographic ranges. Over the past century, they were stocked into new habitats, often with relative disregard for conserving local genetic adaptations. This chapter focuses on their comparative population structure and genetic diversity in relationship to historical patterns, habitat connectivity, dispersal ability, distributional abundances, and reproductive behavior. Both species possess considerable genetic structure across their native ranges, exhibiting similar patterning of discontinuities among geographic regions. The two species significantly differ in levels of genetic diversity, with walleye populations possessing overall higher genetic variability than yellow perch. Genetic divergence patterns follow the opposite trend, with more pronounced differences occurring among closely spaced spawning aggregations of yellow perch than walleye. Results reveal broad-scale correspondence to isolation by geographic distance, however, their fine-scale population structures show less relationship, often with pronounced genetic differences among some nearby reproductive groups. Genetic composition of spawning groups is stable from year to year in walleye, according to two decades of data, and is less consistent in yellow perch. These patterns appear to reflect fundamental behavioral differences between the two species.

Restrictions and closures of commercial freshwater fisheries, coupled with continued high consumer demand, have fueled interest in yellow perch aquaculture. However, the general slow growth of this species and the lack of commercially available broodstocks have been an impediment. A yellow perch broodstock program has been established at the University of Wisconsin Great Lakes WATER Institute in collaboration with the USDA Agricultural Research Service. The goals of this program have been to initiate genetically defined perch broodstocks from several North American geographic regions, characterize their growth, embryonic development and reproduction, and to select these stocks to obtain faster growing fish. This chapter describes the (1) genetic analysis used to define wild yellow perch populations across N. America from which broodstocks could potentially be derived; (2) development and characterization of perch broodstocks from three geographic regions of N. America; and (3) selection of these stocks for enhanced growth and the heritability of that growth.

During the past years, breeding programs for aquaculture have shown fast development. Globally, economically highly relevant species have experienced implementation of large scale breeding programs and it is impossible to imagine life today without them as they significantly improve production and profitability of enterprises. However, there are still many aquatic species cultured that rely on wild broodstock and for which there is no breeding program. The reasons for not having breeding programs are diverse: the knowledge to execute a breeding program is often not available, and more importantly, breeding programs are considered expensive. Costs for separate family rearing systems, testing environments, extensive tagging etc. are often limiting.

Farming of percids is a new sector where pioneering farmers have to develop rearing systems, reproduction methodology, fish feeds, etc., all at the same time. Especially in such cases, low-cost methods are required to get their business up and running. For this reason, many farms consider the foundation of a basic breeding program as their least concern, only to reduce costs. However, we argue that there are good reasons to start with selective breeding at the very start of an aquaculture enterprise.

In the next chapters, the principles of selective breeding programs will be described. This includes a basic description of the concept of estimating the heritable components of the phenotypic appearance of fish. Next the most commonly used selection methods and their implication for percids will be discussed. The potential traits for selection that should be relevant in percid culture are reviewed. Some insights into the optimisation of breeding programs and an overview of basic breeding program management will be presented. We present an outline of how to maintain genetic diversity within cultured stocks, with a special focus on limiting rates of inbreeding while selecting. Finally, some insights on how to manage costs and benefits of breeding programs are discussed.

While there is abundant information about the corticosteroids and the stress response in some fish families such as salmonids, there is little data in percids. Still, despite the scattered information in this fish family, accumulating evidence strongly indicates that corticosteroids are strongly regulated in percids after exposure to stressors and play essential roles in the stress response. This chapter highlights the characteristics of percids concerning the corticosteroid synthesis and receptivity, the basal blood levels, the stressors linked to husbandry conditions conducting to cortisol secretion as well as the secondary and tertiary response to stress with focus on specific biological markers. The usefulness to use cortisol as the best stress marker is discussed and attempts are made to propose other biological indicators of the stress response. The authors will also suggest other ways to prospect the stress response.

Domestication is a process by which animals become adapted to captive life conditions by way of natural and/or artificial selection. Genetic drift and inbreeding may also contribute to the evolution (deleterious or not) of numerous traits during domestication. In fish, domestication has been shown to influence growth, behavior (aggressiveness, dominance, alertness, feeding) and stress responsiveness. With respect to the later, it seems that stress-resistant animals may be selected during domestication as a result of an improved fitness. In percid species, some studies already investigated the effects of several husbandry stressors (chronic confinement, repeated water emersion, single and repeated hypoxia) on the physiological and immune responses along domestication process, by comparing Eurasian perch juveniles from distinct generation levels (Filial 1–5). Under chronic confinement, domestication resulted in a reduction in cellular (HSP70) and physiological (subsequent handling stress) stress response as well as the maintenance of immune status (no decrease in transferrin, complement C3 levels in Filial 4 fish). Domestication did not influence physiological and immune responses to repeated emersion stressor and repeated hypoxia. Eurasian perch has however been shown to be responsive to hypoxic conditions (hyperglycemia, spleen contractions, high transferrin level) and to potentially develop some acclimation mechanism to the repeated disturbance at the expense of some immune functions. All together, the studies demonstrated that domestication positively influenced fish tolerance to chronic confinement but not to hypoxia or water emersion and that this might be linked to the stressor severity. Moreover, F4/F5 fish groups displayed a better immune and physiological status than their F1 counterparts. A microsatellite analysis however revealed that these F4/F5 generations display a lower genetic diversity. Thus, loss of genetic diversity did not appear detrimental to the fish but will nevertheless limit the possibilities of genetic improvement in upcoming generations.

Knowledge of the adaptability of the immune system is an important issue that can enable a better management of environmental conditions for increasing fish performances and welfare. Unfortunately, the immune defence of percid fish has not yet been characterized, but they should be able to accomplish innate and adaptive immunity as other fishes. Indeed, the available information about molecular characterization of some immune genes of percid fish showed similar features as that of other teleost. But some specific pathways were identified; and it could be interesting to precise their implication for the immune competence. It seems also likely that percid fish are able to adapt their immunocompetence to the seasonal changes in environmental conditions, or to respond positively to some immunomodulatory compounds as other fish species, but more studies are still needed to highlight the specific immune pathways of the relative responses.

The farming of perch (

Perca fluviatilis

and

Perca flavescens

) is developing in both Europe and North America and the main infectious diseases associated with these species include viral diseases, such as the perch fry rhabdovirus (PFRv), bacterial diseases such as

Flavobacterium psychrophilum

and

Aeromonas sobria

, protozoan parasites including

Ichthyobodo necator

and myxosporideans such as

Myxobolus neurophilus

. Non-infectious conditions such as tail erosion, gill disease and skeletal deformities also can give rise to significant livestock challenges and welfare problems.

This chapter presents the actual status and the perspectives of development for Eurasian perch and pikeperch in different countries, mainly in Europe (Denmark, Finland, Sweden, Ireland, The Netherlands, France, Czech Republic and Hungary) but also in Iran and Tunisia. For each country, main culture techniques are summarized and production types are specified, according to the local or international markets.

The development of the Percid fish industry calls for reflection on the concept and determinism of quality. This chapter starts with some general considerations illustrating the evolution of quality perception over time. The sense of the word ‘Quality’ is now polysemic; this brings together information about fish characteristics according to their origins (wild versus farmed), but also consideration on how fishes are produced. The complex picture of quality in Percid fishes is here illustrated with the study of nutritional, technological, sensory and sanitary components. We show on the basis of numerous studies that the determinism of quality is multifactorial. Quality components are thus governed by several biological (species, age, genotype, level of domestication…) and environmental (water characteristics, diet, season..) factors. However the quality objectives in Percid Fishes may vary depending on the stakeholders (fish farmer/fisherman, processor or consumer). As far as possible, the various expectations need to be addressed under the target values for the different quality components. In conclusion, we propose the adoption of multifactorial approaches to provide best information in understanding of determinism quality in Percid fishes.

Whilst European perch is consumed in many countries the majority of the market revolves around Switzerland both geographically and in terms of demand and price. Whilst local fisheries such as Lac Leman supply some production, the vast majority of perch consumed in Switzerland is imported. Wild fisheries in Estonia, Poland and Russia supply the bulk of product on the marketplace whilst aquaculture production remains small. The Swiss are not large consumers of seafood but consumption is increasing and perch is likely to remain an important species. However increased consumption of perch is only likely to come on the back of product development and value added offerings as consumers tastes become more refined. The focus on sustainability is particularly important for the Swiss consumer and any production from aquaculture in the future will have to take this into consideration. It is likely in the medium term that large retail multiples will play an increasingly important role in the marketing and sale of perch products. Whilst aquaculture production will likely grow as wild catches decline, it is uncertain whether the market for perch can be extended beyond its traditional base. If market consumption is to increase, considerable resources will have to be invested in consumer education and perception.

Percid farming is still in its infancy; however there are already a handful of commercial ventures successfully producing percids. The underlying factors for success for these companies include the introduction of technology that allows a more intensified production that is independent of season, such as RAS systems and the development of out of season spawning. General know how in these companies and research institutions is also accumulating over time. Continued investment in “learning” has resulted in some companies being able to break the barrier of pilot production and move into commercial production. There are still limitations for further upscaling of production. For established companies these include, domestication, stabilizing and streamlining production, slow growth in larger fish and nutrition. New enterprises find it difficult to find financial backing when there is a lack of general information on Percid markets; basing their sales projections on local traditional market prices. Lack of veterinary knowledge of percids and a working knowledge of RAS systems are also limiting in some countries. Finally, there are recommendations for future development necessary for improving production.