PERCH-LIKE FISHES 125 



Grow to a length of about 2 feet. 



There is probably only one species of Pilot-fish (N. ductor) , 

 with a wide distribution in the open seas of the warmer parts 

 of the globe. It is a somewhat rare visitor to the British Isles 

 during the summer months. Some authorities hold that the 

 Southern Pilot-fish (N. angeli) from Australia, New Zealand 

 and elsewhere, represents a distinct species. 



The inclusion of this comparatively small fish in this book 

 perhaps requires justification, but, since it is so familiar an 

 inhabitant of the open oceans and is so often to be found 

 accompanying ships or large fishes, it may well find a place 

 here. The name " Pilot-fish " is derived from its habit of 

 accompanying ships across the sea and from its frequent 

 association with some of the larger sharks. It has been known 

 to follow a vessel for as long as 80 days. It will generally 

 leave the ship as it approaches land, but has been known to 

 accompany it into harbour. For many years the accepted 

 explanation of its association with the shark was that it acted 

 as a pilot to its companion, which it guided to its food, enjoying 

 in return for this service a degree of protection from its enemies 

 afforded by the presence of its formidable partner. It was 

 also said to share the shark's meal and to feed on the latter's 

 excrements. The fact that small fishes have been found in 

 the stomachs of Pilot-fishes suggests that at times they feed 

 actively on their own account. The association of Pilot-fish 

 and Shark is certainly a very intimate one, and it is a little 

 difficult to understand how this curious partnership comes 

 about. The Pilot-fish seems almost loath to leave its large 

 companion, and, when the shark has been hooked and hauled 

 half out of the water, a number of Pilot-fishes have been 

 described as swimming round and round its tail in an agitated 

 manner. At times they have been observed to retain a more 

 or less constant position near the body of the shark, keeping 

 within a few inches of the base of the pectoral fin. " Fishermen 

 have also noticed," writes Dr. Gilchrist, " that they have the 

 habit of darting away from the shark towards any strange 

 object and then returning to their former position." Two 

 American authors have stated that when accompanying a 

 shark, " they follow their unconscious protector closely, rarely 

 leaving it for many seconds at a time. Occasionally they 



