FOOD. Ixxxix 



observes of the anadromous salmon, herring, and shad, of the United States , 

 of America, that their journeys are simply from the mouths of rivers 

 by the nearest deep gully or trough to the outer sea, and that the appear- 

 ance of the fish- in the mouths of the rivers along the coast at successive 

 intervals from early spring in the south to near midsunimer in the north, is 

 mostly due to their taking up their line of march at successive epochs froni 

 the open sea to the rivers they had left during a previous season, induced 

 by the stimulus of a definite temperature, which, of course, would be 

 successively obtained at later and later dates, as the distance north- 

 wards increased. 



Having ascertained what minute forms or descriptions of life are sought 

 out by migratory fish as food, it next becomes necessary to ascertain what it 

 is that governs or controls their migrations, as currents, soils, temperature, 

 atmospheric changes, or the existence of some still more minute food on 

 ■ which they themselves subsist ; also what are their enemies or their friends, 

 and the conditions which favour the presence or absence of either class. 

 The surface of the ocean everywhere teems to a greater or less extent with 

 aniinal life, but this cannot subsist without a vegetable basis, both being 

 very susceptible to atmospheric vicissitudes. 



When desirous of investigating what constitutes the food of fishes,* it 

 soon beeomes evident that the inquiry branches off in many directions as to 

 whether the fishes are marine or fresh-water, and what districts (page Ixxs) 

 they chiefly frequent : and as researches are extended, the nutriment 

 consumed by the young in their different stages until maturity is attained. 

 While -the fish culturistf and observer will have to find out and ascertain 

 what are the influences which assist in developing the food or act injuriously 

 upon its growth or distribution. Augmenting the numbers of fish in pieces 

 of water is often undesirable without having previously ascertained whether 

 a sufficient amount of food would be present for their wants. 



Among fishes, although we have predaceous, herbivorous, and omnivorous 

 species, there are few which will not prey upon any animal less powerful 

 than themselves, while marine forms are said to be able to withstand hunger 

 longer than those of the fresh waters. The majority of forms feed during the 

 day-time, although some prefer the earlier morning or the evening hours ; 

 others again, as the Liparis, would seem to forage about at night-time. The 

 sucking-fish, Echeneis (page Ixxvii), uses its host as a means of conveyance 

 from place to place, so that it can change its locality : while the myxine 

 consumes its hostj and the electric ray (Ixxvi) takes its prey by nieans 



* See " Food of Fishes," Fishery Conference Papers, F. Day, 1883. 

 t See " Fish Culture," F. Day, 1883. 



