250 THE SENSE-ORGANS AND PERCEPTION OP PISHES. 



of those that are behind makes a dart elsewhere^ when the whole 

 shoal turns round and follows. They certainly have no tendency to 

 follow the largest fish in the shoal^ or indeed any fish in particular. 

 Similarity in size seems to be usual in these shoals. In one of the 

 tanks there are two mullet which have been there for about a 

 year, and are now about three inches long. They live apart on the 

 ledge of the overflow, and never consort with the other mullet, which 

 are about six inches in length. When, however, some of this year's 

 fish (three-quarter inch) were put in, these two immediately swani 

 out to them, and they all retired together into the overflow channel, 

 where they afterwards remained habitually. 



To the fifty small mullet in the long tank I introduced twenty 

 more of rather smaller size, but of the same age, which had lived 

 in another tank. The fifty at once ceased feeding, and huddled 

 timidly away behind the stand-pipe, where they were joined by the 

 new-comers. After a time the latter all left them in a body, thus 

 showing that they recognised each other in some manner. They 

 soon returned, however, and after staying together for a little a 

 detachment of the new-comers again left, and so on ; but on the 

 following day the two shoals had amalgamated and fed together. 

 Weakly fish never swim with the shoal, but keep apart — whether by 

 choice or compulsion could not be determined. 



Two specimens of horse-mackerel [Caranx if rac/iwrus), about two and 

 a half inches long, put in in September, shoaled with the mullet, but 

 the gobies never do so. In November on returning to Plymouth I 

 found that one of the horse-mackerel was dead, and the other had 

 left the mullet and moved about alone, but if alarmed it at once 

 joined the mullet. 



From the fact that the mullet do not move as a shoal at night, it 

 may be so far inferred that they follow each other by sight alone, 

 but it would be interesting to know whether other shoal- fishes travel 

 at night. It may, in fact, be doubted whether such fish as pilchards 

 habitually move about as a shoal at night. Of course drift-netting 

 is carried on at night ; but the nets are shot in places where the 

 pilchards or herrings are known to be, and possibly the slight move- 

 ments of the individuals and currents may take them into the net. 

 That the shoals under some circumstances do not travel at night is 

 seen by the use of the method of seeking pilchards known as 

 " briming " for them. In this operation, which I have never seen, 

 but which has been described to me by several fishermen, as the 

 boat sails along, a man stands on the cuddy and stamps his foot at 

 intervals. When the boat is among the pilchards, they are then 

 seen by means of the '' briming " or phosphorescence to dart away 

 in all directions. Presumably, then, until disturbed by the noise 



