Silvana Duarte

Morphology of gonads, maturity and spawning season of Loricariichthys spixii (Siluriformes, Loricariidae) in a Subtropical Reservoir

A morfologia das gonadas e a epoca de desova de Loricariichthys spixii, no reservatorio de Lajes foi descrita baseada em 175 machos e 613 femeas, coletados de Janeiro-1996 a Dezembro-1997. Celulas de linhagem espermatogenica foram divididas em 4 fases: espermatogonias (primarias e secundarias), espermatocitos (primarios e secundarios), espermatides e espermatozoides, enquanto as celulas de linhagem ovocitaria tambem foram divididas em 4 fases, baseadas em caracteristicas do nucleo, ooplasma e foliculos dos ovocitos: ovocitos primarios (O1), ovocitos previtelogenicos (O2), ovocitos de vesicula cortical (O3) e globulos de vitelo ou vitelogenicos (O4). Cinco estadios gonadais foram descritos para machos/femeas de acordo com a distribuicao das celulas de linhagem ovocitaria / espermatogenicas: repouso (1); maturacao inicial (2a); maturacao avancada (2b); parcialmente esvaziado/desovado (4a); totalmente esvaziado/desovado (4b). Desova e parcelada, ocorrendo atraves do ano. O repouso/recuperacao ocorreu em Julho/Agosto para femeas coincidindo com menores temperaturas e pluviosidades, e diminuicoes do niveis da agua. O amplo periodo reprodutivo e parte da estrategia desenvolvida por esta especie para suportar as pressoes ambientais (bioticas e abioticas) e obter sucesso neste reservatorio oligotrofico e pobremente estruturado.

Reproductive cycle of Parauchenipterus striatulus (Pisces- Auchenipteridae) in the Ribeirão das Lajes reservoir - Brazil

The objective of this work was to evaluate aspects related to the reproductive cycle of the armored catfish Parauchenipterus striatulus in Ribeirao das Lajes Reservoir, state of Rio de Janeiro, Brazil. Gonadal stage, morphology, variations in the gonadosomatic index, weight:length relationship, condition factor and gonadal condition were described. Fish sampling was carried out bi-monthly, between April 1996 and May 1997, using gill nets 100m long, 4m wide, and 25-65mm of mesh sizes gill nets. Three hundred and thirty-nine fishes, corresponding to 40% of the total number, were capture. Five maturation stages were determined by macroscopic analysis of both sexes: immature, mature I, mature II, ripe and spawned (females) or empty (males). The gonadosomatic index was higher from October to March for both sexes, suggesting an ample spawning period, while the condition factor was higher from February to June, showing an inverse relationship between these two characteristics. Weight:length relationship for males was W = 0.0095L3.0862 and for females W = 0.0116L3.0126, with no significant differences between sexes in the allometric coefficient.

Gram-negative intestinal indigenous microbiota from two Siluriform fishes in a tropical reservoir

The Gram-negative intestinal microbiota of Hypostomus auroguttatus and Pimelodus maculatus, a detritivorous and an omnivorous fish species, respectively, were compared between fishes from the reservoir and the stretch of the river below the dam of the Funil hydroelectric plant, Rio de Janeiro, Brazil. Four selective culture media were used under aerobic and two under anaerobic conditions. The omnivorous species had microbiota with higher population levels compared to the detritivorous species. The number of morphotypes and population levels of total bacteria, vibrio and Bacteroides tended to be higher in summer and autumn in the reservoir, and not different in the river. The number of morphotypes of enterobacteria and total bacteria were higher in the lotic environment compared with the lentic one. The bacteria Aeromonas hydrophila and Plesiomonas shigelloides and the obligate anaerobic Fusobacterium mortiferum were the most frequently identified microorganisms in the intestine of both H. auroguttatus and P. maculatus. Both season and habitat influenced the Gram-negative intestinal microbiota of H. auroguttatus and P. maculatus. Environmental factors influenced the Gram-negative intestinal microbiota of both species with possible impact on the interrelationship between the fishes and their digestive ecosystem, although the gut microbiota composition of fishes may result from host-specific selective pressures within the gut.

Reproductive plasticity of Hypostomus affinis (Siluriformes: Loricariidae) as a mechanism to adapt to a reservoir with poor habitat complexity

In this work we describe the gonad morphology and spawning season of Hypostomus affinis (Steindachner, 1877) in a tropical reservoir based on 55 males and 125 females. Our aim was to assess eventual adaptations in reproductive tactics developed by this riverine species inhabiting an oligotrophic reservoir with low habitat complexity, few rocks and few other preferred consolidated substrata. We described the stages of cells of reproductive lineage, gonadal development and some reproductive traits which were compared with information in the available literature. Cells from the spermatogenic lineage were spermatogonia, spermatocytes, spermatids and spermatozoa, and cells from the oocytarian lineage were primary oocytes, previtelogenic oocytes, cortical vesicle oocytes and yolk globules or vitellogenic. Five stages were described for the males/females according to the distribution of oocytes and spermatogenic lineage cells: resting; initial maturation; advanced maturation; partially spent/spawned; totally spent/spawn. Females outnumbered males and reached larger size. Synchronic ovary development in two groups was found with diameter of mature oocytes ranging from 2 to 3.35 mm. Indication of early maturation, a longer reproductive period and the production of smaller eggs in small clutches seems to be features of the reservoir population not found in riverine systems. Such changes in tactics may indicate a shift to an opportunistic strategy, helping the population to withstand environmental constraints and to succeed in this oligotrophic and poorly structured reservoir.

Influence of season, environment and feeding habits on the enzymatic activity of peptidase and β-glucosidase in the gastrointestinal tract of two Siluriformes fishes (Teleostei)

The enzymatic activities involved in the digestion of proteins and carbohydrates were compared among three organs of the digestive track of two Siluriformes fish species, and between two areas: a reservoir, and an area downriver of it. Our aim was to test the hypothesis that the digestive organs of species with varied feeding habits have different enzymatic activities, and that the enzymatic activity differs among seasons and environmental conditions. The iliophagous/herbivorous species Hypostomus auroguttatus Kner, 1854 had higher trypsin-like, chymotrypsin-like peptidase and β-glucosidase activity in the intestine when compared with the omnivorous species Pimelodus maculatus Lacepede, 1803, whereas the latter had more hepatic trypsin-like activity than the former. The peak of activity of the three enzymes in H. auroguttatus was recorded in the winter and spring. On the other hand, P. maculatus tended to have the more prominent peptidase and β-glucosidase activity in the summer, and the smallest in the winter. The intestine of H. auroguttatus had higher enzymatic (trypsin, chymotrypsin and β-glucosidase) activity than the stomach and the liver. For P. maculatus, the highest β-glucosidase activity was found in the liver. The enzymatic activity of H. aurogutattus did not differ between lotic and lentic systems, whereas P. maculatus had comparatively higher stomach and hepatic trypsin levels and hepatic chymotrypsin-like activities in the reservoir than down in the river. These findings indicate that, in H. auroguttatus, most digestive activity occurs in the intestine, which is long and adapted for the digestion of bottom-river vegetable matter and detritus. The seasons and the type of the system (lentic vs. lotic) seem to affect the enzymatic activity for these two species differently, a likely consequence of their different lifestyles.

Enzymatic Activity in the Gastrointestinal Tract of Pimelodus maculatus (Teleostei, Siluriformes) in Two Neotropical Reservoirs with Different Trophic Conditions

Enzymatic activities for digestion of proteins and carbohydrates were compared among three organs of the digestive system of Pimelodus maculatus in two reservoirs with different trophic conditions during the winter of 2006. The aim was to test the hypothesis that enzymatic activity for the digestion of proteins and carbohydrates differed among organs and that such activities differ between the trophic state of the environment. Enzymatic activities were determined through the assays of specificity for trypsin, chymotrypsin and β-glucosidase enzymes. The intestine had higher trypsin-like enzymatic activities compared to the stomach and liver. The highest β-glucosidase activity was found in the liver compared to the stomach and intestine in the oligotrophic reservoir only. Overall, enzymatic activity did not differ between the eutrophic and oligotrophic reservoirs, although the intestinal chymotrypsin was comparatively higher in the eutrophic reservoir and the hepatic β-glucosidase was higher in the oligotrophic reservoir. These findings indicated that most digestive activity occurred in the intestine for P. maculatus, which was probably related to its omnivorous/carnivorous feeding habits. The highest proteolytic activity in the intestine was expected for most fishes, but the high hepatic β-glucosidase in the oligotrophic reservoir was unexpected. The hepatic β-glucosidase as well as the intestinal chymotrypsin-like activity could be considered as the candidates for biomarkers of environmental quality.