No abstract

The reproductive cycle of Trophon geversianus (Pallas 1774) population from Golfo San José (Chubut, Argentina, 42°33 0 S, 64°33 0 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.

Animals frequently face trade-offs between their requirements for maximizing growth and minimizing mortality risk. The partition of habitat use in foraging arenas and refuges as an answer to this trade-off has been evaluated in intertidal crabs but is poorly known in subtidal crabs. The subtidal crab Ovalipes trimaculatus lives and is captured by artisanal fishermen on sandy bottoms of the San Matías Gulf (Lat 41 °S; Argentina). Whereas these bottoms are poor in potential prey, the nearby rocky outcrops are much richer with relatively high abundance of potential prey for the species. Hence, we investigated if crabs in this area are using rocky bottoms as a foraging arena. Stomach content and stable isotopes analysis show that none of the evaluated prey (small teleosts, echinoderms, mollusks and crustaceans) contributed to more than 10% of O. trimaculatus diet, however prey from hard bottoms jointly contributed to 50-80% of the diet. Thus, O. trimaculatus is a generalist carnivore that, despite inhabiting mainly open sandy bottoms, uses rocky outcrops habitats as a foraging arena, probably due to their higher prey availability.