The response of the midgut gland of Artemesia longinaris to salinity changes was evaluated by analyzing its histological changes. Animals were exposed gradually and abruptly to 33, 29, 25 and 16 psu for different time intervals and readapted to 33 psu for 30 days. Individuals maintained 10 days at 16 psu showed the lowest survival and presented histopathologies which were not present in those readapted to 33 psu. Shrimps abruptly transferred from 33 to 16 psu died in 3-5 h but did not show midgut gland alterations likely due to the brief exposure. Only shrimps abruptly transferred from 33 to 25 psu presented histopathologies after 96 h. When readapted to 33 psu for 30 days, the midgut gland recovered an unaltered structure. Except E-cells, which did not vary in height among treatments, F, R and B-cells were taller in animals gradually adapted to 29 than to 16 psu. Abrupt salinity changes had a significant effect on the mean height of F, R and B-cells of those animals transferred from 33 to 25 psu (from 24 to 96 h after transfer F and R-cells heights decreased, and from 96 to 144 h after transfer B-cells height increased). Our study shows the effect of osmotic stress at the tissue level on the midgut gland and, at least partially, explains the reason for the mortalities at low salinities.

Se evaluó la respuesta del hepatopáncreas de Artemesia longinaris a los cambios de salinidad. Los animales fueron expuestos gradual y abruptamente a 33, 29, 25 y 16 psu durante distintos intervalos y readaptados a 33 psu por 30 días. Los individuos gradualmente adaptados a 16 psu tuvieron baja supervivencia y presentaron alteraciones histológicas ausentes en los readaptados a 33 psu. Aquellos transferidos repentinamente de 33 a 16 psu murieron en 3-5 h pero no mostraron alteraciones, posiblemente debido a la breve exposición. Sólo los transferidos repentinamente de 33 a 25 psu por más de 96 h presentaron daño tisular. Cuando se readaptaron a 33 psu durante 30 días, el hepatopáncreas mostró una estructura normal. Exceptuando las células E que no variaron en altura entre tratamientos, las F, R y B fueron más altas en los animales gradualmente adaptados de 33 a 29 psu. Los cambios súbitos de salinidad tuvieron un efecto significativo en la altura media de las células F, R y B solamente en animales transferidos de 33 a 25 psu (24 a 96 h después de la transferencia disminuyó la altura de las células F y R, y 96 a 144 h después hubo un aumento en la altura de las células B). El presente estudio muestra el efecto de los cambios de salinidad sobre el hepatopáncreas y explica, al menos parcialmente, la razón de la mortalidad a bajas salinidades.

Growth, survival, changes in the hepatopancreatic cell morphology, and digestive proteinase activity were evaluated in the red shrimp Pleoticus muelleri (Bate, 1888). A six-week trial was carried out with juveniles of P. muelleri in aquaria. Animals were fed with semi-purified diets with different levels of vitamin A (140, 160 and 180 mg vitamin A kg-1 diet). No differences in survival and weight gain of shrimp were observed among any of the dietary treatments under the experimental conditions. Histological results yielded differences among treatments. In shrimp fed 180 mg kg-1, the functional morphology of the hepatopancreas was normal. Consistent changes with signs of malnourishment, such as cellular hyperplasia and hypertrophy, disorganized tissue, and shrinkage of cells, were evident in the organ of shrimp fed the other diets. The highest proteinase activity was recorded with diets 140 and 160 mg kg-1 and a significant decrease was observed with 180 mg kg-1. It can be stated that optimal level of vitamin A in diets for P. muelleri is 180 mg kg-1 and under malnourishment the hepatopancreas presents structural changes and alterations in protease activity.

Se evaluó el crecimiento, la supervivencia, morfología celular, estructura y la actividad enzimática de proteinasas del hepatopáncreas del langostino Pleoticus muelleri (Bate, 1888). Se realizó un experimento con juveniles en acuarios durante 6 semanas. Los animales fueron alimentados con dietas semipurificadas con diferentes niveles de vitamina A (140, 160 y 180 mg vitamina A kg-1 dieta). No hubo diferencias significativas en supervivencia e incremento en peso en los distintos tratamientos en las condiciones de trabajo. El estudio histológico permitió visualizar cambios estructurales en el hepatopáncreas de los individuos alimentados con diferentes niveles de vitamina A. Los organismos del tratamiento de 180 mg kg-1 presentaron una morfología funcional normal, en cambio en los alimentados con las otras dietas se observó un deterioro del órgano que denota signos de desnutrición, tales como: hiperplasia e hipertrofia celular, desorganización del tejido y retracción celular. La mayor actividad de proteinasas se registró en los tratamientos de 140 y 160 mg kg-1 y se observó una disminución significativa en el de 180 mg kg-1. Se puede concluir que el nivel recomendado de vitamina A en la dieta para P. muelleri es de 180 mg kg-1 y que en situaciones de desnutrición el hepatopáncreas presenta importantes cambios estructurales y alteración en la actividad de las proteasas.

The molt cycle of the natural population of Palaemonetes argentinus Nobili, 1901 from Los Padres Lagoon, Buenos Aires, Argentina, was studied in relation to age, sex, and environmental factors. A total of 1645 individuals (740 females, 539 males, and 366 juveniles) were collected and analyzed between December 1995 and December 1996. The results indicate that the sex ratio (males:females) remains around 1:1.4 throughout most of the year. The reproductive period extends from September until February (spring and summer), with maximum sexual activity in October and November. Two cohorts originated in the spring and in the summer were differentiated. Ovigerous females arrest their molt cycle during the intermolt period to restart it after oviposition. The duration of the intermolt period does not differ between adults and juveniles. Since the percentage of premolt individuals represents 60% of the total cycle, it was classified as a diecdysic cycle. Within the studied range of water temperatures, the observed variations in the span of the different stages, indicate that this factor does not alter the molt frequency. Like in the rest of decapods, the intermolt duration of P. argentinus is modified by ovarian maturation.

The paper deals with the aspect related to the growth and methods used to estimate the size and weight increment of the Decapod crustaceans in the Argentine Sea (Southwest Atlantic Ocean). At first are mentioned the endocrine mechanism which promote and control the molting cycle. Comments are made on the characteristcs of the discontinuous growth in crustaceans, depending on successive moults, i.e. changes of the exoskeleton. Details are given of the methods used by different authors, especially those on argentine species, including some methods quantitative of analysis of growth. Examples are given for sexual dimorphism and secondary sexual characters, permanent or transitory, which are related to the reproductive cycle in some species. Finally, influences of environmental conditions on growth are reviewed: temperature, ligth, salinity, pressure, pollution and other factor related to nutrition, limb loss, and parasitism

trabajo se refiere a los aspectos biológicos del crecimiento y a los métodos empleados para estudiar el aumento de tamaño en los crustáceos Decápodos del mar epicontinental argentino. Primeramente se reseñan los mecanismos endócrinos que controlan y desencadenan la muda. Luego se describen las características distintivas del crecimiento en los crustáceos, que se produce en forma discontinua y sujeto a las sucesivas mudas (cambio del exoesqueleto). Se mencionan los métodos usados por distintos autores, especialmente los referidos a especies argentinas, incluyendo algunos de los métodos cuantitativos empleados en Argentina para analizar el crecimiento. Se presentan ejemplos sobre el dimorfismo sexual y caracteres sexuales secundarios permanentes o transitorios relacionados con el ciclo reproductivo de algunas especies. Finalmente, se destaca la influencia de las condiciones ambientales (temperatura, salinidad, contaminación) y de otros factores tales como la nutrición, la pérdida de apéndices y el parasitismo sobre el crecimiento