Ana María Petriella

Influence of dietary fatty acids and cholesterol on the growth and survival of the Argentine prawn, Artemesia longinaris Bate

Abstract The influence of essential fatty acids and cholesterol on the growth and survival of the Argentine shrimp Artemesia longinaris, was tested using experimental pelleted diets based on a standard diet. A series of diets were designed and prepared by adding cholesterol, pure oleic acid, raw linseed oil and fish oil (rich in fatty acids of the ω 3 series). After 30 days, no significant differences in growth were registered among the animals fed different rations, although significant differences in survival were found. The best survival was obtained with the diet supplemented with fish oil (87.3%). Survival of prawns fed the other diets was significantly lower (53.3–56.7%). Animals fed low fat diet, showed the lowest survival (30%). The results indicated the importance of cholesterol in the diet, and stressed the dietary necessity of highly unsaturated fetty acids of the linolenic acid series for the optimal survival of A. longinaris.

Functional cytology of the hepatopancreas of Palaemonetes argentinus (Crustacea, Decapoda, Caridea) under osmotic stress

The present work describes the effect of different salinities on the functional morphology of the P. argentinus hepatopancreas and analyses the tissue recovery after re-acclimation to freshwater. Adult prawns of both sexes at sexual rest were collected from a tributary of the Mar Chiquita coastal lagoon. The prawns were acclimated in aquaria to four salinity conditions: 0 (control), 8, 16 and 24‰. To evaluate the possible tissular recovery, after 60 days individuals from all the treatments were gradually acclimated to freshwater and maintained for other 30 days. Hepatopancreas samples were processed at the beginning of the trial and every 30 days using standard histological techniques for OM and TEM. The individuals from all the treatments, except the controls, showed a continuous weight decrease, and survival was lower when higher the salinity. At 30 days from the beginning of the experiment, hepatopancreas from 16 and 24‰ salinities showed an enlarged tubular lumen and an infolded basal lamina. Ultratructurally, nuclear retraction, cytoplasmolysis, and RER membranes separated with electron-dense content were observed in all the treatments except 0‰. After 60 days, profound alterations were observed with the three treatments. After the re-acclimation period, there was no reestablishment of the functional cytology. The tolerance to short-term salinity changes explains the capability of this prawn to inhabit in estuarine environments.

Morphological and functional study of the male reproductive tract in the shrimp Pleoticus muelleri bate (Decapoda, Penaeoidea)

Summary Anatomical relationships and the histological structure of the male reproductive tract in Pleoticus muelleri were described by using light microscopy. The male reproductive tract consists of paired organs: testes and vasa deferentia with the terminal ampoule, which opens at the gonopores on the coxae of the fifth pair of pereopods. Testes are located dorsally in the cephalothorax and are comprised of two lobes surrounded by laminar connective tissue. They are composed of cystic structures (with spermatogonia or primary spermatocytes) covered by connective tissue. Each vas deferens consists of four morphologically different zones: the collecting tubule, proximal, medial, and distal (terminal ampoule). The collecting tubule connects the testes with the proximal zone and is lined by a shallow epithelium. The proximal zone, lined by a columnar secreting epithelium, is internally divided into two ducts by a septum. The biggest spermatophoric duct conveys the sperm mass, and the other secretes the acellular material that supports the sperm mass in the spermatophore. In the medial zone the ducts are incompletely separated by a partial septum and the epithelial cells secrete the hyaline layer of the spermatophoric matrix. The distal zone or terminal ampoule comprises four interconnecting chambers and is externally surrounded by connective tissue and a conspicuous layer of striated muscle. The spermatophore reaches complete maturation in the terminal ampoule.

GROWTH OF THE PRAWN, PALAEMONETES ARGENTINUS NOBILI, 1901 (DECAPODA, PALAEMONIDAE) ON DIFFERENT FEEDS

Our aim was to study the individual growth of Palaemonetes argentinus in the laboratory, and to analyse the effect of diet on both moult increment and intermoult period. Juveniles collected from Los Padres lagoon (38°S 55°W) were maintained individually in 400 ml containers with aerated fresh water under a constant regime (19 ± 2°C; 11 : 13 h L/D) and fed daily. Three different feeds were given: frozen shrimp (76% proteins, 17% lipids) and two formulated diets, i.e., E(0.5) and M91 (containing 45 and 54% proteins, and 17 and 14% lipids, respectively). The moult increment was studied by comparing premoult and postmoult weight and cephalothorax length, and by next determining a linear regression according to Kurata (1962), which resulted in an arithmetic growth with the M91 diet (b = 0.96) and geometric regressive growth with E(0.5) (b = 0.94) and shrimp (b = 0.88) for the weight values. Length data yielded geometric regressive growth, with coefficients of 0.91, 0.79, and 0.91 for E(0.5), M91, and shrimp regimes, respectively. The average duration of the intermoult period was: E(0.5), 16 ± 2 days; M91, 18 ± 2 days; frozen shrimp, 18 ± 3 days. Comparing survival, moulting rate, and growth, the prawns grew best under the M91 dietary regime. These results indicate that, in this species, a food with approximately 50% protein and with a high proportion of animal-based ingredients produces satisfactory growth and survival. Se estudio el crecimiento individual de Palaemonetes argentinus en laboratorio, analizando el efecto de la dieta sobre el incremento por muda y el periodo de intermuda. Se mantuvieron individualmente camarones juveniles obtenidos de la laguna de Los Padres (38°S 55°W) en recipientes de 400 ml con agua dulce aireada y bajo condiciones constantes de temperatura y fotoperiodo (19±2°C; 11 : 13 h L/O). Se alimentaron diariamente probando tres alimentos: camaron congelado (76% de proteinas, 17% de lipidos) y dos dietas formuladas, E(0,5) y M91 (conteniendo 45 y 54% de proteinas y 17 y 14% de lipidos, respectivamente). El incremento por muda se estudio comparando el peso y la longitud del cefalotorax premuda y postmuda, analizando su ajuste a distintos modelos de regresion lineal de acuerdo con Kurata (1962). A partir de los datos se determino un crecimiento aritmetico con la dieta M91, con un coeficiente de crecimiento en peso b = 0,96; geometrico regresivo con E(0,5) (b = 0,94) y camaron (b = 0,88). En cuanto al crecimiento en longitud fue geometrico regresivo con las tres dietas, con coeficientes de 0,91, 0,79 y 0,91 para E(0,5), M91 y camaron, respectivamente. La duracion promedio del periodo de intermuda fue: E(0,5), 16±2 dias; M91, 18±2 dias; camaron congelado, 18±3 dias. Comparando la supervivencia, la tasa de muda y el crecimiento, los camarones crecieron mejor con la dieta M91. Estos resultados indican que, para esta especie, una dieta con aproximadamente 50% de proteinas totales con una alta proporcion de proteinas animales produce un crecimiento y una supervivencia satisfactorios.

Molt cycle of the natural population of Palaemonetes argentinus (Crustacea, Palaemonidae) from Los Padres Lagoon (Buenos Aires, Argentina)

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.

Gill morphology and ultrastructure of the prawn, Palaemonetes argentinus Nobili, 1901 (Decapoda, Caridea)

A morphological and ultrastructural study was performed on the gills of Palaemonetes argentinus from the Sotelo stream, a tributary of the Mar Chiquita coastal lagoon (Argentina, 37°45′S 57°26′W). This species possesses a phyllobranchiate gill, in which the central axis is triangular and has one row of flattened lamellae on each side. There are one afferent channel, two efferent channels, and several tegumental glands along the axis. Nephrocytes are only present in the stem, associated with the efferent haemolymph. Mature nephrocytes have a voluminous vacuole, surrounded by satellite vacuoles, a lateral nucleus, and pedicels on the surface. In the lamellae, the principal cells have apical extensions with deep infoldings and a neck-like zone with bundles of microtubules. The nucleus is in a basal expansion of the cell and the basolateral membranes of neighbouring cells are interdigitated, with large numbers of mitochondria in the interdigitations. The cells show characteristics of both respiratory and ion-regulatory epithelium; they also have a structural role in directing the haemolymph flow and in supporting the lamellae. The thicker cuticle near the marginal channel increases mechanical support. The ultrastructure of the lamellar epithelium appears to be related to the capability of P. argentinus of living in freshwater and adapting to media with variable salinity. Se realizo un estudio morfologico y ultraestructural de las branquias del camaron Palaemonetes argentinus del arroyo Sotelo, tributario de la laguna costera de Mar Chiquita (Argentina, 37°45′S 57°26′W). Esta especie posee filobranquias, cuyo eje central tiene forma triangular y posee una hilera de laminillas aplanadas a cada lado. Hay un canal aferente, dos canales eferentes y glandulas tegumentarias a lo largo del eje. Se observaron nefrocitos asociados con la hemolinfa eferente en el eje central. Los nefrocitos maduros tienen una vacuola voluminosa rodeada por vacuolas satelite, un nucleo lateral y pedicelos en la superficie. En las laminillas las celulas principales tienen extensiones apicales con profundos pliegues y una zona mas estrecha con numerosos microtubulos. El nucleo se ubica en una expansion basal y las membranas basolaterales de las celulas vecinas se interdigitan encerrando numerosas mitocondrias. Estas celulas muestran caracteristicas de un epitelio respiratorio y osmorregulador. Tambien tienen una funcion estructural: dirigen el flujo de la hemolinfa y proporcionan sosten a las laminillas. La cuticula engrosada en el canal marginal incrementa el sosten mecanico. La ultraestructura del epitelio de las laminillas parece estar relacionada con la capacidad de P. argentinus de vivir el agua dulce y de adaptarse a ambientes con salinidad variable.

Estructura del aparato reproductor masculino de Uca uruguayensis (Decapoda, Ocypodidae)

El objetivo de este trabajo es describir las estructuras del sistema reproductor de machos de Uca uruguayensis Nobili, 1901 y estudiar los cambios relacionados con la madurez sexual. Se trabajo con observacion estereoscopica de material fresco, tecnica histologica de rutina y observaciones en Microscopio Electronico de Barrido. Se incluyo la caracterizacion de los gonopodos 1 (G1) y 2 (G2). El tracto reproductor del macho se compone de un par de testiculos (T), un vaso deferente (VD) tubular y sinuoso y una ampolla terminal (AT). El VD tiene tres secciones, la anterior (VDA), la media (VDM) y la posterior (VDP). El VDA y VDM estan conformadas por un epitelio simple de celulas cubicas. El epitelio del VDP es columnar y con nucleos basales y alongados. El diseno tubular se modifica al ocuparse el lumen del VDP con liquido espermatico durante el verano y la musculatura circular se hace mas evidente. La porcion terminal del VDP se ensancha formando una ampolla (AT) que comprende cuatro camaras interconectadas. Todas las estructuras estan rodeadas de una capa de tejido conectivo de poco espesor. Se identifican las modificaciones observadas en la histologia de T y VD, definiendo como mas relevantes las observadas desde el mes de noviembre hasta marzo. Estas modificaciones sugieren que U. uruguayensis tiene, en la localidad estudiada, una unica estacion reproductiva durante el verano en esta latitud. La AT, tal como es descripta, es una estructura que hasta el momento no ha sido mencionada para los Brachyura.

Cytoarchitecture of the Hepatopancreas of Three Species of Crabs from Mar Chiquita Lagoon, Argentina

Based on the various functions of the crustacean hepatopancreas, this work analyzes the possible structural differences in brachyurans from different microhabitats in the Mar Chiquita lagoon “cangrejal” (37° 45′ S, 57° 26′ W). Adult males in intermolt (Stage C) of Uca uruguayensis, Chasmagnathus granulata and Cyrtograpsus angulatus were collected at the same time. The hepatopancreas was removed and processed by using standard histological techniques. The organ completely occupies the dorsal hemocoel in C. granulata and C. angulatus, while it is arranged in two dorsal, lateral masses in U. uruguayensis. The cytoarchitecture of the three species is similar to that observed in other brachyurans. Differences in the tubular structure are related to the presence of a peritrophic lamina in all its extension and a marked differentiation at the medial zone in C. angulatus. The tubular lumen in C angulatus and U. uruguayensis is cross-shaped, though very branched in C. granulata. These characteristics indicate a different rhythm in the cycle of cellular activity. The tubular and cell dimensions are similar for the three species; it is outstanding the augmented intertubular tissue in U. uruguayensis.

Efecto de la ablacion peduncular en la maduracion gonadal de Pleoticus muelleri bate (decapoda, solenoceridae). I. interaccion entre muda y desarrollo ovarico

Este trabalho teve como objetivo comparar o grau de desenvolvimento ovariano de remeas ablacionadas e intactas de Pleoticus muelleri e avaliar a influencia da ablacao sobre a frequencia da muda. As femeas, de 7 a 22 g de peso, foram mantidas em condicoes de cultivo com fotoperiodo de 12:12, temperatura entre 15 e 17ÂoC, salinidade de 31 e alimentadas com lula, camarao e bivalvos frescos. Foram pesados e fixados os ovarios e hepatopâncreas, realizando um controle histologico nos 4; 9; 15; 20; 40 e 50 dias. O indice gonadossomatico variou entre 0,925 e 3,747 (controle) e entre 1,457 e 5,035 (ablacionados). Determinou-se valores de indice hepatopancreatico entre 2,059 a 4,520 (controle) e de 3,471 a 4,471 (ablacionados). A duracao media da intermuda foi 21,7 :j: 3,9 e 23,2 :j: 2,4 dias para o grupo controle e ablacionados, respectivamente. Ao finalizar o experimento a analise histologica demostrou que os ovarios das femeas ablacionadas encontravam-se totalmente amadurecidos e os do controle em vitelogenese primaria. Conclui-se que a ablacao peduncular acelera a maturacao ovariana de P. muelleri, sem modificar a frequencia da muda. O indice ovariano e independente do tamanho no intervalo de peso estudado e a ablacao nao apresentou efeito sobre o peso relativo dos hepatopâncreas.