Venerus et al .: Early life history of Pseudoperas semifasciata 



197 



A total of 68 preserved larvae, ranging in body length 

 (BL) from 3.3 to 11.7 mm, were used to describe larval 

 development. Terminology for morphometries followed 

 Neira et al. (1998). Additionally, head depth (HD) was 

 defined as the maximum depth of the head. Preserved 

 larvae were measured to the nearest 0.1 mm with an 

 ocular micrometer fitted to a dissecting microscope, 

 and their pigmentation pattern was recorded. Possible 

 shrinkage was not considered in the measurements. 

 Whenever possible, the number of vertebrae and num- 

 bers of dorsal, anal, caudal, pectoral, and pelvic fin rays 

 were recorded. In addition, 14 larvae from 3.4 to 11.7 

 mm BL were cleared and stained following the methods 

 of Potthoff (1984) and Taylor and Van Dyke (1985), and 

 then examined for meristics and osteological features. 

 Myomere and fin-ray counts and morphometric measure- 

 ments were made on the left side of the body. Larval 

 abundance was expressed as the number of larvae/ 

 10 m 2 of sea surface as recommended by Smith and 

 Richardson (1977). 



Posttransition juveniles 



Posttransition juveniles were collected with a small 

 bottom trawl called "Piloto," with the following features: 

 6 m total length, 6-m headrope and groundrope, 25-mm 

 wing mesh size, 10-mm codend mesh size, 0.25-m 2 otter 

 board surface and 12 kg weight, 10-m bridles and 0.80- 

 m vertical opening. In Argentina, commercial fishing 

 vessels use this gear for locating shrimp concentra- 

 tions. Additionally, an epibenthic sampler (Rothlisberg 

 and Pearcy, 1976) fitted with 1-mm mesh was used on 

 one cruise (EH-02/92). We believe that individuals up 

 to 12 cm total length were well represented in samples 

 obtained with this gear. 



A total of 27 posttransition juveniles, ranging from 

 22 to 83 mm body length (BL), were used to describe 

 Argentine sandperch developmental stages. Samples 

 were either frozen or fixed in 5% formalin to seawater 

 solution. Measurements and degree of pigmentation 

 were recorded after preservation. 



Total length (TL), body length ( = standard length), 

 head length (HL), predorsal length (PDL), and preanal 

 length (PAL) were measured to the nearest 1 mm. Head 

 depth (HD), body depth (BD), and eye diameter (ED) 

 were measured to the nearest 0.2 mm. Three juveniles 

 between 22 and 33 mm BL were cleared and stained 

 (Potthoff, 1984; Taylor and Van Dyke, 1985) and exam- 

 ined for meristics. 



The density of posttransition juveniles, expressed as 

 individuals/square nautical mile (nmi 2 ), was estimated 

 from swept area. The family Pinguipedidae includes two 

 species (morphologically very similar as juveniles) that 

 overlap in the Argentine Sea. Unfortunately, not all 

 individuals caught during the cruises were examined 

 by us; therefore, to avoid biases caused by identifica- 

 tion errors, the posttransition juveniles of both species 

 were considered as a group. Distributional centroids 

 and ellipses were calculated by following the method 

 of Kendall and Picquelle (1989), that is by weighting 



each station by the density of juveniles caught. For this 

 purpose each density value was standardized with re- 

 spect to the maximum density observed for each survey 

 season over all years. 



Results 



Description of larvae 



General morphological features The larval body was 

 elongate and relative BD was <25% in all stages of 

 development (Table 2). The smallest larva collected 

 (yolksac larva) was 3.3 mm BL. Its yolk sac was small 

 and the single oil globule was located on the anterior 

 part of the yolk mass. Notochord flexion began at 6 

 mm and was complete by 7-8 mm BL. As development 

 proceeded, larvae became slightly deeper and laterally 

 compressed. The head was small, with a rounded snout 

 and no spines. The oblique mouth was open by the end of 

 the yolksac larval stage. By 10 mm BL, premaxilla and 

 dentary bones were covered with caniniform teeth. The 

 premaxilla was an elongated bone with three processes 

 on its dorsal margin — the first one perpendicular to the 

 premaxilla. Relative head length remained constant, 

 whereas relative head depth diminished during develop- 

 ment (Fig. 1). The eyes were pigmented and their relative 

 diameter decreased during the preflexion stage, and 



