PÓS-MARSUPIAL LIFE CICLE AND GROWTH OF METAMYSIDOPSIS ELONGATA ATLANTICA (CRUSTACEA, MYSIDACEA, MYSIDAE) UNDER LABORATORY CONDITION.Metamysidopsis elongata atlantica (Bacescu, 1968) was reared in the laboratory for 45 days at 20±1°C and salinity of 30ppt. Growth curves (von Bertalanffy model) were calculated for both sexes and for each sex. The daily rate of carapace growth was significantly different between females and males (F test, p <0.05). Before the sexual maturity (14 days), the growth rate of females was higher than that of males (females, 0.0457 mm day -1 ; males, 0.0448 mm day -1 ). After the maturity (15 to 45 days), these rates decreased similarly for both sexes (females, 0.0203 mm day -1 ; males, 0.0174mm day -1 ). The average growth rate was 0.0207mm day -1 over the 45 days. Twelve molts were observed in a period of 60 days. The first five molts occurred up to 14 days old (age of the sexual differentiation), with a mean intermolt period of 2.9 days. From the 6 th molt it increased to 5.6 days. The results suggest that the use of the carapace length is a good measure to calculate the growth and longevity of the organisms.

ABSTRACT. Metamysidopsis atlantica elongata (Bascescu, 1968) is a common mysid in the surf zone of sandy beaches from the state of Rio Grande do Sul, Brazil, where it is frequently recorded forming dense aggregations. Trough laboratory trials, behavioral responses to salinity (10, 20, 25, 28, 30, 40 e 45), temperature (10, 15, 20, 30±1°C) and light (yes/no) were tested using adult males, adult females and juveniles. Although there was no response to temperature, the species showed clear response to salinity and light. In the presence of light, organisms remained in the bottom of the aquaria, but moved to surface when bottom salinities were increased. In the absence of light, adults moved to the surface. However, juveniles moved down to or remained on the bottom, maybe as a response to avoid adult predation. KEYWORDS.Mysids, behavior, light, predation. RESUMO. Respostas do comportamento nictimeral deMetamysidopsis elongata atlantica (Crustacea, Mysida) a gradientes de salinidade e temperatura. Metamysidopsis elongata atlantica (Bascescu, 1968) é um misídeo comum na zona de arrebentação de praias arenosas do Rio Grande do Sul, Brasil, onde aparece constantemente formando densas manchas. Em laboratório, respostas comportamentais a salinidade (10, 20, 25, 28, 30, 40 e 45), temperatura (10, 15, 20, 30±1°C) e luz (sim/não) foram testadas usando machos adultos, fêmeas adultas e juvenis. Embora não tenha ocorrido resposta à temperatura, as espécies mostraram respostas claras à salinidade e luz. Na presença de luz, os organismos permaneceram no fundo do aquário, porém se moveram para a superfície quando as salinidades do fundo aumentaram. Na ausência de luz, os adultos se moveram para a superfície do aquário. No entanto, os juvenis desceram ou se mantiveram no fundo, provavelmente como uma resposta para evitar a predação dos adultos.

ABSTRACT. Moulting cycle and growth rate of Metamysidopsis elongata atlantica (Crustacea, Mysidacea) reared at different temperatures and salinities. Metamysidopsis elongata atlantica (Bascescu, 1968) was reared in the laboratory at different combinations of temperature (13, 20, and 25°C) and salinity (25, 30, and 35‰) to estimate the intermoult period and carapace growth rate. Temperature affected both intermoult period and growth rate of the animals. Mysids reared at 13°C had longer intermoult periods than those reared at 20 and 25°C. While animals reared at 13°C had the longest longevity, females did not develop marsupium when reared at this temperature. Growth rate estimated for mysids aged between 0 to 14 days (age at the onset of maturity) was 0.02 mm/day, 0.04 mm/ day, and 0.05 mm/day for animals reared at 13°C, 20°C, and 25°C, respectively. KEYWORDS.Crustacea, Mysidae, Metamysidopsis elongata atlantica, growth rate, molts. (Bascescu, 1968) foi cultivada em laboratório em diferentes combinações de temperatura (13, 20, and 25°C) e salinidade (25, 30, and 35‰) para estimar o período de intermuda e a taxa de crescimento da carapaça. A temperatura afetou o período de intermuda e a taxa de crescimento dos animais. Misidiáceos criados a 13°C tiveram maiores períodos de intermuda que aqueles cultivados a 20 and 25°C. Enquanto animais criados a 13°C tiveram maior longevidade, fêmeas não desenvolvem marsúpio quando cultivadas nesta temperatura. A taxa de crescimento estimada para misidáceos entre 0 a 14 dias (idade no início da maturidade) foi 0,02 mm/dia, 0,04 mm/dia, e 0,05 mm/dia para animais cultivados respectivamente a 13°C, 20°C e 25°C. RESUMO. Metamysidopsis elongata atlantica PALAVRAS-CHAVE.Crustacea, Mysidae, Metamysidopsis elongata atlantica, taxa de crescimento, mudas.