Is a cannibal different from its conspecifics? A behavioural, morphological, muscular and retinal structure study with pikeperch juveniles under farming conditions

Influence of the source of spawners' origin on oocyte maturity stages and suitability for artificial reproduction of wild pikeperch (Sander lucioperca) females during spawning season

Pikeperch is one of the major new fish species in freshwater aquaculture. Artificial reproduction is difficult in this species, and many aspects require further study. These include synchronization of female maturation, latency time, gamete quality and spawner survival rate. For these reasons, many fish farmers must constantly replenish their spawning pikeperch stock, often with wild fish. Data on the suitability for the reproduction of wild fish obtained in several lakes during the reproduction period were collected in this study. The findings indicated that larger fish (> 1.5 kg BW) and those obtained in larger and deeper lakes (> 12.0 m mean depth vs. < 5.0 m mean depth, respectively, for deep and shallow lakes) were more valuable to fish farmers during the spawning season when they were obtained because a higher percentage of suitability for artificial reproduction and a higher embryo survival rate was observed for them. The mean embryo survival rate was high and was 84.5 ± 3.9 % on the 3rd day after fertilization and 79.7 ± 3.4 % at hatching. Among the group of the smallest females (< 1.5 kg), the highest percentage of nonsynchronous oocyte maturation occurred. This result demonstrated the successful procedure of both artificial reproduction and a successful method for selecting females for spawning.

Enrichment in a Fish Polyculture: Does it Affect Fish Behaviour and Development of Only One Species or Both?

Physical enrichment of structures has been used for the last decades in aquaculture to improve fish production and welfare. Until now, this enrichment has been practiced in fish monoculture but not in fish polyculture. In this study, we developed a polyculture of two freshwater species (pikeperch and sterlet) in recirculated systems (tank of 2.4 m3) with or without physical structures for enrichment. Two types of structures were used: a cover plank on a part of the tank decreasing the light intensity and vertical pipes modifying the water flow. The experiment was conducted in triplicate for a three-month period with juvenile fishes (143 ± 41 g and 27.3 ± 2.2 cm for pikeperch and 133 ± 21 g and 32.8 ± 1.6 cm for sterlet). Behavioural (space occupation and abnormal behaviours) and morphological (total length, final weight, Fulton condition factor, coefficient of variation of the final weight, percentage of biomass gain and specific growth rate) traits were measured. The pikeperch changed their space occupation and showed a preference for low light areas. Sterlet also changed their space occupation: they did not use the cover and occurred mainly in the part of the tank without enrichment. There was no difference for the frequency of abnormal behaviours for pikeperch and sterlet between the two sets (with or without enrichment). There was no statistical difference between the two sets for all the morphological and growth parameters no matter the species and the rearing modality.