Control of good quality eggs and larvae takes into account the influence of some factors such as temperature, photoperiod, nutrition, stocking conditions,… Up to now, in Percid fishes, it has been demonstrated that gamete quality of captive breeders constitutes one of the principal limiting factor in the production of these species, even more when fish are fed with an artificial dry diet. It has been demonstrated that the dietary fatty acid content might affect the physiology of breeders and their reproductive performances. Therefore, the general objective of the thesis was to understand the mecanisms implicated in the preferential utilization of dietary fatty acids in relation to changes in lipid metabolism, as well as to endocrine changes linked to maturation observed during a reproductive cycle in Percid females, with Eurasian perch as biological model. Indicators of sperm quality were also investigated. We have studied the impact of polyunsaturated fatty acids on the physiology of reproduction, both in vivo and in vitro. The results showed that AA, via its conversion to PGE2 and PGF2 alpha, may have a stimulating role in the oocyte maturation, by enhancing some maturation-inducing steroids, such as the maturational hormone. As observed in mammals, we concluded that the cAMP production in response to PGE2 was probably mediated by an intracellular mechanism via the EP2 receptor. Nevertheless, in our study, the production of PGE2 and PGF2 alpha was conditioned by the EPA/AA ratio in fish tissues, which is dependent upon the EPA/AA ratio found in the diet. Vitellogenin production was also depending on the EPA/AA ratio, with values fluctuating in a similar manner to what was obtained with prostaglandins, just before the spawning season. Sperm and eggs fatty acid compositions were dependent on the fatty acid content of broodstock diet, while indicators of sperm quality were all good in fish fed diets with a high or low DHA/EPA/AA ratio, and egg and larval quality were both affected by the diet given to breeders. So it can be concluded that female gamete quality was more sensitive to the dietary DHA/EPA/AA ratio than the male one. A study of fertilizing ability should be conducted to definitely confirm this statement. A dietary imbalance of highly unsaturated fatty acid is certainly responsible for the lower egg and larval quality observed for some diets. Indeed, reproductive performances were characterised by lower spawning, fertilizing and hatching rates for fish fed a high EPA/AA ratio compared to a ratio of 1, and larval resistance after an osmotic stress was also lower. In all the experiments, the relative levels of AA and DHA were maintained in eggs, whatever the tested diet, except in eggs of fish fed a commercial food for salmonids (DHA/EPA/AA : 14/16/1). This diet provided the lowest egg and larval quality, with only 26% fertilization rate, 15% hatching rate and 100% of larval mortality at the end of the osmotic stress. This suggests that AA and DHA present in eggs conditioned the correct hatching and fertilization rates, and also the larval survival. The essential fatty acid requirement from the n-3 series for Eurasian perch breeders is 18:3 n-3, since perch is clearly able to elongate and desaturate 18:3 n-3 into HUFA, while for the n-6 series, AA is definitely required. Providing 18:2 n-6 as the only source of n-6 PUFA is not sufficient since it has been shown that AA is particularly needed during maturation and spawning due to its important role as eicosanoids precursor. All in all, it can be hypothesized that the best dietary DHA/EPA/AA ratio tested is 2/1/1 for Eurasian perch breeders in order to obtain good egg and larval quality.
- Perche
- lipides
- aquaculture
- nutrition
- reproduction
Effects of dietary n-3 and n-6 polyunsaturated fatty acids on the lipid metabolism and on reproductive physiology and performances of Eurasian perch breeders (Perca fluviatilis)
Henrotte, E. (Auteur). 2 déc. 2009
Student thesis: Doc types › Docteur en Sciences