Effect of various commercial diets on rearing performance, body chemical and fatty acid composition, liver histology and vertebral column anomalies in Eurasian perch (Perca fluviatilis L.) post-larvae

The effects of three commercial diets (AF PE and PP) that differed in nutritional value on growth, cannibalism and survival in Eurasian perch post-larvae were performed. Of the feeds used, the PE feed contained a lower level of crude protein and a higher level of crude fat with a higher level of saturated fatty acids (SFA) and a lower level of polyunsaturated fatty acids (PUFA) than the AF and PP feeds. Additionally, chemical composition, including the fatty acid (FAs) content of perch body, liver histology and vertebral column anomalies relative to tested diets were analysed. It was shown that the two-month perch fed by diet with the highest fat content and the lowest protein content (PE) achieved significantly higher weight and body length. During the experiment, a relatively higher survival was obtained in perch groups fed with PE and PP feeds. Significantly lower type II intra-cohort cannibalism in perch fed with two diets (PE and PP) was observed, which probably resulted from better assimilation and, consequently, a sense of greater satiety in fish (PE diet) and faster perception by perch of its presence in the experimental system (PP diet). Moreover, the increase in type II cannibalism in perch fed with the AF diet could be due to the poorer palatability of this feed (understood in terms of its availability). The results of our study confirmed the hypothesis that the level of fat in the body of fish depended on the level of crude fat from feed used; however, it was also found that the fatty acid composition of the perch body was irrespective of the content of FAs in the diet used. Our data suggest that differences in the level of proximate and FAs compositions in tested commercial diets do not affect the histological structure of the liver and the prevalence of skeletal malformation in Eurasian perch post-larvae.