Aspects of the biology of Nezumia aequalis from the continental slope west of the British Isles

Nezumia aequalis is one of the most abundant fishes on the upper and middle continental slopes (500-1750 m depth zones) of the North-east Atlantic with a peak abundance of three to four individuals 1000 m(-2) swept area in the 750-m zone. Mean and modal size increased with depth, fish from the Rockall Trough (RT) being larger than those at equivalent depths in the Porcupine Seabight (PSB). Sex ratios were close to parity in all depth zones. Females grew larger than males. Head length to total length and to total weight did not differ significantly between sexes but RT fish were heavier at any given length than PSB fish. Serial batch spawning occurred over the first three quarters of the year. Ovaries contained five size groups of eggs, the three largest groups being vitelline and contributing 27% of the absolute individual fecundity which was positively correlated with body size and ranged from 9109 to 26 847. Age determined from sagittal otoliths ranged from 1 to 10 years, the ageing method being validated by a time-series study of the growing edge of otoliths. The von Bertalanffy growth parameter (k) was estimated at 0.175 and 0.216 from head length and otolith length, respectively. (C) 1999 The Fisheries Society of the British Isles.