VALIDATION OF AGE READINGS FROM OTOLITHS OF JUVENILE ROUNDNOSE GRENADIER, CORYPHAENOIDES RUPESTRIS, A DEEP-WATER MACROURID FISH

Validation of the ageing of deep-water fish is difficult and there are only a few instances where the rings on the otoliths have been shown to be laid down annually. Roundnose grenadier have been fished commerc ially in the North Atlantic since the 1960s and the adult fish have fr equently been aged by counting the rings in otoliths or scales. All th e ageing was done on the assumption that the rings in the otoliths or scales were annual. Between 1975 and 1992, the Scottish Association fo r Marine Science carried out seasonal trawling surveys in the Rockall Trough using a fine-meshed trawl, and collected otoliths from a wide s ize range of roundnose grenadier. An examination of the growing edge o f otoliths from juvenile fish From these collections suggests that the rings in the otoliths are laid down annually. The broader, opaque zon es which represent the growth phase were dominant between September an d March. The thinner, hyaline zones were dominant between April and Ju ly. The apparent delay in the growth phase compared with most shallow- water species is discussed in relation to the availability of mesopela gic prey. (C) 1996 The Fisheries Society of the British Isles