ROLE OF ETHOLOGY 247 



It is time now to ask: Can useful and valid inferences be drawn 

 from ethological observations on oceanic animals made under 

 restricted aquarium conditions? 



As the outcome of suggestions made at a meeting of the Inter- 

 national Council for the Exploration of the Sea at Amsterdam in 

 1951 (Bull, 1952) a research assistant, Aliss V. AI. Brawn, joined 

 me at Cullercoats to make a study of the behavior of Gadus 

 callarias, the most important commercial fish of European waters. 

 What follows is the result of a joint endeavor but is mainly her 

 work. It is put forward here to illustrate the kind of ethological 

 approach which can be profitably used in the study of economically 

 important marine animals. We have already reported briefly upon 

 it (Bull and Brawn, 1959) and further papers will shortly be 

 published by her. 



Patient observation over two years of large numbers of healthy 

 specimens (ranging in size from 7 cm to 70 cm), many of w^hich 

 lived throughout the period of observations and were known 

 as individuals with their own code letter, enabled Miss Brawn 

 (1957) to establish a number of ethological facts which have rele- 

 vance to this discussion. There is time to summarize only a few of 

 these. Cod develop a social hierarchy and an order of dominance 

 through aggressive behavior which has not been previously de- 

 scribed. This occupies a large part of their daily life. It includes a 

 number of subsidiary actions, a fast approach, and a full threat 

 display, and variations in their intensity; per contra there are the 

 intimidating effects produced, such as flight and fear postures of the 

 socially inferior individuals. Loud grunts of a frequency of less than 

 50 cps either singly or in 2, 3, or 4 often accompany aggression and 

 flight; these again have not been described before but they are a 

 significant feature of the cod's daily and seasonal activity. 



Aggression is at its peak in late summer and autumn, and there 

 is another outbreak during February and March at actual spawn- 

 ing time. At the times when there is no aggression, from after 

 spawning to the beginning of July and again from December to 

 the end of January mature fish swim freely in all parts of the 

 aquarium without exciting aggression. During aggressive periods 

 fish which are being continually put to flight by other more 

 aggressive ones come to show fear of these in other situations. A 



