Vitellogenesis and changes in lipid and protein content of oocytes of Trophon geversianus (Neogastropoda: Muricidae) in Golfo San Jose (Chubut, Argentina)

The reproductive cycle of Trophon geversianus (Pallas 1774) population from Golfo San José (Chubut, Argentina, 42°33′S, 64°33′W) was studied using histochemical methods and digital image analysis. For such purpose, ovary samples were taken monthly between July 2006 and August 2007 and stained with hematoxylin and eosin, Sudan black B (to identify lipids) or Schiff’s ninhydrin (to identify proteins). Four different gametogenic stages were described: oogonias, previtellogenic oocytes, early vitellogenic oocytes, and late vitellogenic oocytes. Two spawning events were registered; one between September and October 2006, and a second one between February and March 2007. Oocyte quality was determined by the changes in lipid and protein composition during gametogenesis. Through digital image analysis, a lipid and a protein indexes (LI and PI) were calculated. Significant differences were observed in LI over month sampled, contrarily to what PI showed. A significant and positive correlation was found between lipid and protein content and oocytes areas, indicating that these nutrients accumulate during the entire vitellogenesis. Also, when dividing the oocytes into two size groups, analysis indicates a positive correlation between LI and oocyte area for smaller area oocytes. This demonstrates that while proteins accumulate linearly throughout vitellogenesis process, lipids accumulate in two steps: first at a growing rate, secondly at constant rate. This information is essential to determine the nutritional requirements of brood stock individuals at hatcheries in this potential fishery resource that inhabits patagonian waters.