Hammer, H.S.*; Watts, S.A.; Lawrence, J.M.; Lawrence, A.L.; McClintock, J.B.: The effect of dietary protein concentration on gonad composition and gametic condition in the sea urchin Lytechinus variegatus

Ecological studies suggest that nutrition, particularly dietary protein, affects nutrient storage and reproductive competency. Starved urchins (ca. 36 mm diameter, n=12) were held in replicated (3x) 80 L aquaria with artificial seawater at 21 C and 32 ppt salinity for each diet treatment. The urchins were fed one of three isocaloric diets containing 14 (L), 32 (M) or 50% (H) protein ad libitum for a 10-week period. The mean gonad index increased from 0.3 to 10.7, 11.3, and 12.7 for the L, M, and H protein diets, respectively. The gonad contained 25.7, 31.2, and 41.2% protein and 47.3, 39.7, and 24.6% carbohydrate for the L, M, and H protein diets, respectively. Lipid level averaged 19-22 % and did not vary significantly with diet. Histological evaluation of ovaries suggest that females fed a H protein diet had increased gametogenic activity in the germinal epithelium and larger numbers of mature and maturing oocytes as compared to those fed a L protein diet. Similarly, males fed a H protein diet had increased gametogenic activity in the germinal epithelium; those individuals fed a L protein diet appeared to resorb numerous gametes. Individuals fed a H protein diet had nutritive phagocytes containing a hematoxylin-positive, protein-rich cytoplasm; in individuals fed the L protein diet the cytoplasm appeared to contain dispersed protein granules. These data indicate that the proximate composition of the gonad reflects the composition of the diet. Dietary protein affects gametogenic activity and the composition of the nutritive phagocytes. Funded by Mississippi-Alabama Sea Grant.