Abundância, distribuição e caraterização morfológica de larvas de Atherinella brasiliensis (Atherinopsidae,Atheriniformes) no estuário do rio Jaguaribe,Pernambuco, Brasil

Abstract

This study presents information about Atherinella brasiliensis larvae from the Jaguaribe river estuary, located in the northern coast of the state of Pernambuco, northeastern Brazil. Its objective was to characterize the abundance and distribution of larvae, along with a description of their external morphology and morphometric data. Ichthyoplankton samples were taken monthly, from April 2001 to April 2002, through surface towing of a 500μm conical-cylindrical plankton net, at six different sampling stations. Temperature and salinity average values ranged, respectively, from a minimum of 17.44 and 27.26ºC in January and June, to a maximum of 37.73 and 29.90oC in December and April. A total density of 258.04 larvae.10m-3 was recorded throughout the study period, 94.23% of which were in the preflexion stage. Higher larvae densities were recorded in October, January and March, and lower in September. Among stations, higher densities were recorded in the upper reaches of the estuary, which presented low and quiet waters. A. brasiliensis larvae hatch with an average standard length (SL) of 1.4mm. In the preflexion stage, the body is envolved by a finfold, beginning just behind the head, and four dendritic chromatophores are present on top of the head. The flexion stage begins with a SL of 3.8mm, dorsal and anal fins present pterigyophores and the mouth is terminal, but somewhat upward orientated. With 4.7mm SL, the larva is at the end of the flexion stage and beginning of postflexion. In the postflexion stage, an ossification of dorsal and anal fin rays is evident, as well as the pelvic buds and darkening of lateral pigmentation. With approximately 12.0mm SL, all fins are formed, and the second dorsal one is the last to be formed, being located posterior to the anal. The juvenile stage begins at approximately 15mmSL. In this stage, A. brasiliensis present the anal fin located at the body midpoint, and the posterior end of pectorals surpasses the pelvic fin origin, which is located at an equal distance from the pectoral and anal fins’ origins. Scales are clearly visible at the dorso-lateral region, behind the head. The results indicate most of the species life cycle takes place in the estuary, it presents multiple spawning, and initial recruitment occurs in January and March. The morphological features herein described allow the identification of its larvae, together with an adequate differentiation from hemiramphids and other atheriniform species.