CONDITIONS OF LIFE 245 



To eat and to avoid being eaten by others are the most 

 important factors in the daily Hfe of a fish, and certain species, 

 in order to further these ends, have taken to associating with 

 other fishes, or have entered into partnership, as it were, with 

 other animals. Such associations are generally to the advantage 

 of the fish, but frequently for the mutual benefit of both parties. 

 The little Pilot-fish (Naucrates) provides an example of one type 

 of association, and has derived its name from the habit of 

 accompanying ships and large fishes, particularly Sharks. It 

 is a small oceanic species, rarely exceeding fifteen inches in 

 length, and is found in practically all warm seas (Fig. 940). Its 

 general coloration is bluish above and lighter below, and the 

 body is crossed by broad dark bands. It is common in the 

 Mediterranean, and was well known to the ancients under 

 the name of Pompilus. Most of the accounts of this fish given 

 by Greek or Roman writers refer to an association with whales 

 and dolphins rather than with sharks, and Aristotle refers to 

 it as the "Dolphin's louse." It was credited with the power of 

 guiding sailors lost upon the ocean, and of announcing the 

 vicinity of land by its sudden disappearance. 



For many years it has been accepted that the Pilot-fish is in 

 the habit of guiding Sharks to their food, enjoying in return a 

 degree of protection from its enemies by the proximity of its 

 formidable companions, but it seems clear that many observers 

 have been led astray by sentiment, as well as by the tendency 

 of some people to ascribe human emotions to all the lower 

 animals. It is quite true that one or more of these fishes are 

 usually to be found accompanying Sharks, and that they will 

 also follow slow-moving ships for considerable distances, but it 

 is more than likely that the fragments of the Sharks' meals or 

 the food thrown overboard from the ships provide the attraction, 

 and that their immunity from attack is due solely to their 

 exceptional agility which enables them to avoid being caught 

 by the Sharks. The Pilot-fish does not always leave a ship as 

 land approaches, and in warm weather they have been known 

 to follow vessels as far as the south coast of England, even 

 accompanying them into harbour on occasions. The fact that 

 some individuals have been caught with their stomachs full 

 of small fishes suggests that they do at times pursue their prey 

 on their own account. 



In the case of the Shark-sucker or Remora {Echeneis) already 

 described {cf. p. 70) the association between the two fishes is 

 more intimate, and is of a type known as commensalism. 



