Hake

Abstract: Daily growth increments have been found in otoliths of fish larvae. The daily nature of these layers was verified by examining larval fish of known age reared in the laboratory. A simple technique for observing these marks is described and can be used on otoliths from larvae and adults. This provides a convenient method for determining early growth in fishes and is particularly useful for fishes which do not lay down annual or seasonal rings. The use of otoliths in age determination (by means of annual marks) is well known. The techniques used have been described by Williams and Bedford (1974) and Blacker (1974). Recently Pannella (1971) has suggested that daily marks may be formed in the sagittae (the otoliths used almost universally in age determinations) of some temperate species, while in 1974 Pannella claimed to have detected them in a number of tropical species. He also studied the temperate species-silver hake, Merluccius bilinparis; red hake, Urophycis chuss; Atlantic cod, Gadus mrhua; and winter flounder, Pseudopleuronectes americanus-in greater detail in this latter paper. For some of these temperate species, particularly for the first, Pannella was able to show that there were fortnightly, monthly, and annual patterns. The annual marks detected in the conventional way were shown to contain about 365 daily units. Pannella used acetate replicas of ground otoliths which had been previously etched with HC1. Pannella’s work appears to justify the following conclusions: