Larval and juvenile development of Tatia intermedia (Siluriformes: Auchenipteridae)

This study describes the morphology, morphometry and meristic characters of larval and juvenile Tatia intermedia collected in the middle Tocantins River and some of its tributaries. Six larvae of T. intermedia were examined and they have a moderately elongate body, head slightly dorso-ventrally depressed with a convex snout, small and round eyes and a subterminal mouth. In five juvenile stages observed, the head and eye are relatively smaller than in the larval stage and the snout remains convex and mouth becomes terminal.

Diel vertical migration and spatial overlap between fish larvae and zooplankton in two tropical lakes, Brazil

The effect of fish larvae on the diel vertical migration of the zooplankton community was investigated in two tropical lakes, Finado Raimundo and Pintado lakes, Mato Grosso do Sul State, Brazil. Nocturnal and diurnal samplings were conducted in the limnetic region of each lake for 10 consecutive months from April 2008 to January 2009. The zooplankton community presented a wide range of responses to the predation pressure exerted by fish larvae in both environments, while fish larvae showed a typical pattern of normal diel vertical migration. Our results also demonstrated that the diel vertical migration is an important behaviour to avoid predation, since it reduces the spatial overlap between prey and potential predator, thus supporting the hypothesis that vertical migration is a defence mechanism against predation.

Spatial and temporal distribution of larvae and juveniles of Hoplias aff. malabaricus (Characiformes, Erythrinidae) in the Upper Paraná River floodplain, Brazil

Spatial and temporal distribution of larvae and juveniles of trahira, Hoplias aff. malabaricus (Erythrinidae), and their relationship with environmental parameters in the Upper Paraná River floodplain were analyzed. Sampling of larvae and juveniles of H. aff. malabaricus has been conducted during the period from November 1991 through February 1995, with 42 sampling stations distributed in four sub-areas: Ivinhema I, Ivinhema II, Baía, and Paraná. During the same period, data were obtained for water temperature, dissolved oxygen, pH, electrical conductivity, river level, precipitation index, and photoperiod. The largest catches of larvae were in the Ivinhema I sub-area (47.06%), and of juveniles in the Paraná sub-area (54.55%). Larvae and juveniles were caught from October to February. Larvae were mainly collected at night and in all types of environments sampled (lotic, semi-lotic, and lentic). Principal Component Analysis of the environmental parameters and larval density showed that the largest catches were obtained in dry season months, with low values for temperature, electrical conductivity, river level, and photoperiod, and with high concentrations of dissolved oxygen and pH. This reproductive strategy may minimizes predation and maximizes food utilization, as it enables the fish to reach advanced developmental stages, while most other species are spawning.