Ph.D. Thesis by Abi-Ayad S.-M., Faculty of Science, University of Liege, Belgium
Abstract:
In this experimental work, the interaction between reproduction and nutrition were studied in Perca fluviatilis broodstocks. The nutritional aspect concerned the (n-3) polyunsaturated fatty acids, specially the docosahexaenoic fatty acid 22:6n-3 (DHA) requirements in perch breeders. The reproductive aspect concerned the organs and fatty acid mobilisation during maturation, embryonic and larval development, and the impact of these micro-nutrients on egg and larval quality.
The muscle and the peri-visceral fats were alternatively mobilised in perch broodstocks during the ovarian maturation. However, lipids from liver were mobilised during the entire maturation period due to its important role in the biosynthesis of vitellogenin, the egg-specific lipoprotein. The fatty acids mobilised from the differents organs were catabolized for providing energy or used for vitellogenin biosynthesis. However, the DHA fatty acid is entirely transferred and incorporated with vitellogenin in the growing oocytes.
The lipid and fatty acids were not catabolized for providing energy in perch embryonic development. During the larval development, only monounsaturated and polyunsaturated fatty acids were catabolized. The contribution of these two classes of fatty acids was 50%-50% and 40%-60% during starvation and the first week of feeding respectively. Thereafter, the catabolized energy from fatty acid was issued from feed instead of body. The use of DHA was different between starved and fed larvae. In starved larvae, the contribution of DHA as energy source was only 3% while it reached up to 25% in fed larvae.
The DHA requirements of Perca fluviatilis during gonadal maturation was 0.9% of the dry feed. This concentration was sufficient to produce eggs and larvae characterised by higher fecundation (86%) and hatching (75%) rates and an increased resistance to osmotic shock (17.7%) and extended starving (L.D. 50=169 hours). Below (0.3-0.6%) or above (1.5%) the perch broodstock produced eggs and larvae with lower fecundation (52-62%) and hatching (45-49%) rates and a decreased resistance to osmotic shock (0.9-7.4%) and extended starving (L.D. 50=99-116 hours).
In late spawning, the quality of eggs and larvae was lower compared to the ones obtained earlier. There was no relationship between egg and larval quality and the fatty acid composition of eggs. Moreover, eggs produced by 2-years old perchs spawning for the first time exhibited a lower fecundation and hatching rates than those produced by 3-years old perchs spawning for the second time. The poorer fecundation and hatching rates were not correlated with the fatty acid composition of eggs. Other factors potentially responsible of this quality decrease are debated.