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The freshwater crab Aegla platensis was used as a model to induce ovarian growth by adding different neuroregulators to a pellet food formulation. Added compounds were the dopaminergic inhibitor spiperone or the enkephalinergic inhibitor naloxone, both of them at a dose of 10-8 mol/animal. Animals were fed on the enriched pellets twice a week. After 7 wk, the gonadosomatic index (GI) was calculated as (gonad fresh weight / body fresh weight) x 100. GI significantly increased only for those females fed on spiperone pellets, compared to a control group receiving pellets with no compound added. During the assayed period, spiperone would be reverting the arrest exerted by dopamine on the neuroendocrine stimulation of ovarian growth. On the other hand, for both spiperone and naloxone a higher GI was correlated to a higher lipid content of both gonads and/or hepatopancreas, suggesting an increased energetic demand in accordance with an active investment in reproduction.

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We compared the eff ect of diff erent diets in the biochemical composition, levels of lipoperoxidation and survival rates of males and females of Hyalella bonariensis . Th ese crustaceans live in limnetic environments and diff erent kinds of food habits are present in the genus Hyalella . Adult animals were collected in the spring (September) in a stream near to Salto city, Buenos Aires. In the laboratory, the animals were kept submerged in aquariums, separated by sex, under controlled conditions and survive rates were observed. Th ey were fed ad libitum for 45 days with four diff erent diets, and after this period the animals were used for biochemical determinations. Statistical analysis revealed signifi cant diff erences in the responses to glycogen, proteins, lipids, triglycerides and lipoperoxidation levels in both sexes of these amphipods taken from the natural environment. Animals that received macrophytes associated a ration with high content of proteins (43%) during 45 days presented the major survival rates (males= 86.6% and females= 96.6%). Th ese responses can be revealed that this specie primarily feeding macrophytes associated with deposit feeder, and that this diet is more generalized. Th is study showed the importance of the proteins in diet of this amphipod, were the females increased the reserves of proteins and triglycerides with diff erent diets probably for reproductive events and male increased the reserves of glycogen and triglycerides for reproductive events and growth.