The length-weight relationship and spatial, temporal and ontogenetic changes in the condition factor of Micropogonias furnieri (Desmarest, 1823) were analyzed, from samples collected between October 1998 and September 1999, in the Sepetiba Bay, a coastal area with a wide communication with the sea (22º54'-23º04'S, 43º34'-44º10'W) at Southeast Brazil. The aim was to supply basic information on the form of growth of the population of M. furnieri that uses the bay, as well as to assess changes in the fish condition. Most fish were young and subadults. The length-weight equation, based on 2499 unsexed individuals, was Wt = 0.009095 * Lt2.99, where Wt is the total weight (g) and Lt is the total length (cm). The regression constant and the regression coefficient presented significant inverse relationship (p < 0.01), indicating that the regression coefficient from the length-weight relationship is not a good parameter for characterizing different populations, because its strong association between one another. The best condition was recorded in October/November and April, and the worst, between January and March. Spatially, the best condition was observed in the inner bay zone, where most fish were young-of-the-year, and in the outer zone where predominate larger sized fish, indicating that individuals of intermediary size could be allocating large amount of energy for growth, presenting, consequently, lowest condition. Isometry was detected for M. furnieri populations at Sepetiba Bay, and variations in physiologic condition could be associated to feeding availability, mainly in the inner zone, where the harsh water quality would not be constrained for development of this species

The white croaker Micropogonias furnieri is a commercially important marine fish that uses bays and other semi-closed coastal areas early in its life. A sampling programme, using beach-seine and otter trawl, was carried out in Sepetiba Bay (22°54′–23°04′S, 43°34′–44°10′W), southern Brazil, from October 1998 to September 1999, with the objective of assessing the patterns of temporal and spatial usage of the bay by white croaker during its early life. Early recruits (total length, TL, 10–50 mm) appear off beaches of the inner bay between October and December, move away from them during late summer and early autumn (January–April), and are caught by trawl offshore from May to September at a TL of 70–150 mm. From May to August, new recruits (10–50 mm) are again found inshore. Fish grow from 10–40 to 70–150 mm during the first year of life in the shallows of the bay, before moving offshore. They cross the deeper waters of the bay as they migrate towards the open ocean. Juveniles (TL 70–150 mm) are most abundant in the inner bay, and subadults (TL 150–200 mm) in the outer and central bay. M. furnieri use semi-closed coastal areas as nursery grounds, before moving out over the continental shelf, where they spawn.

We sampled fish and measured environmental variables in the Sepetiba Bay, a tropical embayment at Southeastern Brazil. The aim was to assess environmental influences on distribution of four abundant species of Sciaenidae Micropogonias furnieri (Desmarest, 1823), Ctenosciaena gracilicirrhus (Metzelaar, 1919), Cynoscion leiarchus (Cuvier, 1830) and Menticirrhus americanus (Linnaeus, 1758) to test the habitat partition hypothesis. Samples were taken between June 1993 and July 1996, at three bay zones (outer, central and inner). Depth was the most important environmental variable to influence fish distribution, followed by transparency. M. furnieri showed significant negative correlation to depth, transparency and salinity, while C. gracilicirrhus showed the opposite situation. The highest densities of C. leiarchus occurred in the lowest temperature, while M. americanus did not showed preferences for any of the examined environmental variables. Spatial separation, mainly between M. furnieri and C. gracilicirrhus, seems to be the strategy developed to coexist in the Sepetiba Bay, with M. furnieri being more adapted to copy with harsh environmental conditions of the inner bay. The other three species, which use mostly the outer bay zone, seem to be restricted to more stable conditions, where influences from oceanic waters are more intense.

We determined in this study the habitat preferences of seven native fish species in a regulated river in Southeastern Brazil. We tested the hypothesis that fishes differ in habitat preference and that they use stretches of the river differing in hydraulic characteristics and substrate type. We surveyed fishes in four 1-km long river stretches encompassing different habitat traits, where we also measured water depth, velocity, and substrate type. We investigated preference patterns of four Siluriformes (Loricariichthys castaneus, Hoplosternum littorale, Pimelodus maculatus, and Trachelyopterus striatulus) and three Characiformes (Astyanax aff. bimaculatus, Oligosarcus hepsetus, and Hoplias malabaricus), representing approximately 70% of the total number of fishes and 64% of the total biomass. We classified fishes into four habitat guilds: (1) a slow-flowing water guild that occupied mud-sand substrate, composed of two Siluriformes in either shallow (< 4 m, i.e., H. littorale) or deep (> 8 m, L. castaneus) waters; (2) a run-dwelling guild that occurs in deep backwaters with clay-mud substrate, composed of the Characiformes A. aff. bimaculatus and O. hepsetus; (3) a run-dwelling guild that occurs in sandy and shallow substrate, composed of T. striatulus; and (4) a fast-flowing guild that occurs primarily along shorelines with shallow mud bottoms, composed of H. malabaricus and P. maculatus. Our hypothesis was confirmed, as different habitat preferences by fishes appear to occur in this regulated river.Determinamos neste estudo a preferência de habitat de sete espécies de peixes abundantes em um rio regulado do Sudeste do Brasil. Testamos a hipótese de que peixes diferem na preferência de habitat e usam trechos do rio com diferentes características hidráulicas e tipos de substratos. Realizamos amostragens de peixes, utilizando redes de espera e tarrafas em quatro trechos do rio de 1 km de extensão, compreendendo diferentes características do habitat, onde também obtivemos medidas de profundidade, velocidade da água e tipo de substrato. Quatro Siluriformes (Loricariichthys castaneus, Hoplosternum littorale, Pimelodus maculatus e Trachelyopterus striatulus) e três Characiformes (Astyanax aff. bimaculatus, Oligosarcus hepsetus e Hoplias malabaricus) que juntos compreenderam aproximadamente 70% do número total e 64% do peso total de peixes foram estudados. Classificamos os peixes em quatro guildas: (1) peixes que ocorrem em trechos com baixa velocidade de fluxo e substrato constituído predominantemente de lama e areia, compreendendo dois Siluriformes, um de áreas rasas (< 4 m, i.e., H. littorale) e outro de áreas profundas (> 8 m, i.e., L. castaneus); (2) peixes que utilizam rápidos de áreas laterais mais profundas com substrato lamoso, representados pelos pequenos Characiformes, A. aff. bimaculatus e O. hepsetus; (3) peixes que utilizam rápidos que ocorrem em áreas rasas e substrato arenoso, representado por T. striatulus; e (4) peixes de corredeiras que utilizam as margens rasas com fundo lamoso, representados por H. ...