22 



THE SCIENTIFIC AND ECONOMIC ASPECTS 



evidence to show that this fish does not feed indiscriminately 

 upon any form of the plankton it may happen to encounter. 



The view advanced by previous authors upon general 

 ichthyology that certain surface feeding fishes, e.g., mackerel 

 and some members of the Clupeidae, obtain their food supply 

 by means of a process of filtration, has given rise to a more 

 or less general belief that the action of feeding is a passive 

 and involuntary one. 



In the case of herring and mackereP^ frequenting the 

 English Channel it has already been shown that a certain 

 capability for selective feeding does exist, which may extend 

 to organisms of minute size. But since undue generalization 

 upon the habits of nearly allied species of fish affords no reli- 

 able basis of argument, we have to consider those observa- 

 tions alone bearing relation to the pilchard. 



Perhaps the most valuable observation in support of any 

 theory of this selective capability being exercised by pilchards 

 in feeding is that made by Cunningham-^ upon larval fish 

 reared at Plymouth. This author states : " On the fifth day 

 (after hatching) I put some of the minute creatures gathered 

 from the sea by the tow-net into the tank containing the larvae, 

 and also some minute particles of minced sea worms, and they 

 began to feed. When five days old the larvae . . . were seen 

 to peck or strike at the particles, which they swallowed. So 

 that feeding is a deliberate and active, not a passive involun- 

 tary process." It is only fair to suppose that if such a 

 capability for selective feeding were known to be exercised by 

 any species of fish at such an early age, it would be developed 

 the more strongly in the later stages of its growth. The evi- 

 dence which we at present possess in support of such a theory 

 so far as it affects the adult fish, may be regarded as negative. 



It has already been shown that throughout the present 

 investigation it has not been found possible in any instance to 

 determine the presence of the same number of plankton species 

 in a stomach as that occurring in tow-nettings taken on the 

 same position from whence the fish were derived. Generally, 



23 BuUen, G. E., " Some notes upon the Feeding- Habits of Mackerel and 

 certain Clupeoids in the English Channel " (Journ. M.B.A., Vol. ix., No. 3). 

 2^ Cunningham, J. P., "Mark. Mar. Fishes," p. 173. 



