Influence of dietary protein on essential fatty acids in the gonadal tissue of the sea urchins Psammechinus miliaris and Paracentrotus lividus (Echinodermata)

The elevated accumulation of certain essential long-chain polyunsaturated fatty acids (PUFA) during reproductive maturation can place a significant demand on lipid metabolism. As lipid metabolism is closely linked with protein metabolism, protein intake during maturation may significantly influence transport proteins and enzyme activity which is responsible for supplying the essential fatty acids for gamete development. The present study investigated the influence of increased protein intake on the accumulation of certain long-chain PUFA in two species of commercially valuable sea urchin, Paracentrotus lividus and Psammechinus miliaris during maturation. Sea urchins were fed three macroalgal diets over a 90-day period. These diets included the red alga Palmaria palmata, which had been grown in seawater enriched with two levels of ammonia-N, which produced a high protein content (41%) or low protein content (32%). The third diet (or reference diet) used the brown macroalga Laminaria saccharina with a 23% protein content. The fatty acid composition of the gonads was determined by GC. Feeding the high protein diet had no effect on the maturation and total lipid in the gonad compared with the low protein diet, however, it did significantly increase the levels of docosahexaenoic acid DHA 22:6n-3 in the mature gonad tissue in P. miliaris and P. lividus. In contrast, only P. miliaris exhibited higher levels of arachidonic acid ARA 20:4n-6 when fed the high protein diet. The present study suggests that elevated protein levels can promote the accumulation of DHA and ARA in gonadal tissue during maturation, although the extent of the influence is species-specific and highlights the importance of understanding the complexities and inter-connectivity between protein and lipid metabolism when producing commercially valuable species.