Two species of codlet (Bregmacerotidae) larvae were collected during nine survey cruises conducted in the south‐eastern Brazilian Bight between 23oS and 30oS in 1985‐91. Of 4846 codlet larvae collected during nine cruises, 99.2% were identified as Bregmaceros canton and only 0.8% were B. athanticus. The two species were more abundant during winter in the neritic region (60–135 m depth). Vertical distribution of codlet larvae was studied using the BIOMOC net, and vertical profiles of temperature/salinity and chlorophyll a concentration were recorded by CTD and fluorescent sonde. Only 9.0% of larvae were collected in the upper 30 m and 91.0% were found deeper (> 40 m). The depths of highest density of larvae bore a close relationship to the subsurface chlorophyll maximum layer. Some B. canton larvae were found in the upper 30 m layer at night, but no larva was found during the day. Water temperatures where B. canton larvae occurred ranged from 16 to 23oC, but most larvae were found at 18–20oC and in salinities of 35.5–36.5 psu.

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The pearlside Maurolicus stehmanni is one of the most abundant mesopelagic fishes off south‐eastern Brazil and plays a key role in the regional ecosystem. However, its early life history remains poorly understood. This study examined the M. stehmanni early life stages, from eggs to juveniles, including all developmental changes in external morphology. Larvae are simple in morphology and lack specialized larval structures. Notochord flexion begins at ~5.15 mm body length (BL) and larvae ≥5.95 mm BL are flexed. The relative growth of seven measured larval characters (head length, body depth, snout length, eye diameter, pre‐dorsal length, pre‐ventral length and pre‐anal length) have transition points (allometric inflexion points), indicating biphasic growth patterns which are likely related to shifts in habitat use, feeding and behaviour. Larval development is similar to that of other Maurolicus species. The relatively fast development of the fins, photophores, swimbladder and pigmentation suggests a precocious adoption of a micronektonic lifestyle in the mesopelagic environment.

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