SEA-FISHERIES LABORATORY. 165 



is itself a stimulus to growth, and reproduction, and to the 

 maintenance of a condition of health. 



The shallow- water grounds off the coast, between low- 

 water mark and about 5 to 10 fathoms of depth, are therefore 

 the place of origin of all the young fish in this neighbourhood. 

 For about three years the plaice of the Irish Sea live here 

 moving a little out to sea in the warm summer months and then 

 returning inshore again for the period of the winter and spring. 

 They roam about to a marked extent, making quite long, winter, 

 longshore migrations, possibly in search of food and possibly 

 just from the general " restlessness " that is a fundamental 

 feature of animal life. In certain months, about December to 

 March, there is an evident scarcity of the small plaice on the 

 nursery grounds, and it is highly probable that they " dawk " 

 in the sand at the bottoms of the deeper, inshore channels, 

 covering themselves up so that only the mouth is visible. 

 Respiration slows down, the fish cease to eat, and their functions 

 are as nearly at a standstill as possible. The weight of the 

 body, in proportion to the length, decreases. If we call w the 

 body- weight in grams, I the total length in centimetres, and 

 c a constant, then we get the following formula : 



100 P 



c = 



w 



Now when we find the value of c for the various months 

 throughout the year we see that it varies from about 0-8 to 1-2. 

 When it is small, at the period of about lowest sea- temperature, 

 the plaice is thin and in poor condition, and when it is large, 

 at about the period of highest sea- temperature, in the autumn, 

 the fish become plump. The decrease in the magnitude of c 

 means that the fish does not feed and that the substance of 

 its body is being used up to keep the heart and respiratory 

 organs in action. Therefore there is a wasting of the body 

 during the coldest months of the year. 



