Caracterização do desenvolvimento ontogênico inicial de Anchoviella vaillanti (Steindachner, 1908)

Abstract

This study aimed to describe morphologically the ontogenetic initial development of the freshwater anchovy, Anchoviella vaillanti, which is endemic to the São Francisco river basin. We analyzed 132 specimens (SL = 1,3-51 mm) obtained from hauls made with a 500 μm mesh conical-cylindrical plankton net in quarterly samplings in different stretches of the Sobradinho reservoir from January 2002 to January 2004. Individuals were classified into the following phases: larvae – yolk-larval,preflexion, flexion and postflexion stage - and juvenile. We measured the morphometric data, standard length (SL), preanal length (PAL),prepelvic length (PPVL), prepectoral length (PPL), predorsal length (PDL), head length (HL), head depth (HD), eye diameter (ED), and body depth (BD). Some specimens were cleared and stained for evidencing and detailing internal structures, counting of preanal, postanal and total vertebrae, pectoral (P), dorsal (D), pelvic (V), anal (A) and caudal ( C) fin rays and the relative position of dorsal and anal fins insertion. During the larval stage, the body ranged from very elongate to elongate, and the head and the eye both from small to moderate. In juveniles, body varied from elongate to moderate, the head was moderate, and the eye from moderate to large. Prefin lengths in relation to SL ranged from 61.5 to 79.2% for PAL; 51.8 to 72.9% for PDL; 10.7 - 29,2% for PPL and 37.8 - 47, 2% for PPVL. HL ranged from 7.9 - 29,2%; HD from 5.7 - 19.2%; BD from 6.3 to 27.1%; and ED from 16.7 - 42.9% HL. The total vertebrae number in A. vaillanti ranges from 36 to 39 and myomere number ranges from 31 to 45. Dorsal fin insertion varies between the 14th and the 18th precaudal vertebrae and the anal fin insertion varies between 21st and 24th precaudal vertebrae. The sequence of first fin ray formation was D, C, A, V and P. The final number of rays among them, however, is attained in the following order: D and A in the flexion stage and P, V and C in the postflexion stage. In the lower São Francisco River, A. vaillanti may occur sympatrically with A.lepidentostole and may be distinguished by the lower number of dorsal fin rays (15-16 versus 12-13 in A. vaillanti), lower vertebrae count (40 versus 37-40) and greater pre-pectoral length(14-16 % SL versus 22,8-28,9% SL).