XC MIGRATION AND FOOD. 



of shocks. Under the head of each species I have endeavoured to give an 

 account of the food each is most partial to. While in captivity some fish eat 

 what they reject or are unaccustomed to when in a state of natui'e : 

 some forms in aquaria will consume, if they can obtain it, more than is 

 wholesome for them. 



If .we look at a newly-hatched fish we see a large sac or the yelk or 

 umbilical-sac dependent from its throat, in it noui'ishment is contained on 

 which it has to subsist for a longer or shorter period, and when absorbed it 

 must seek food for itself, and this in the period when the fish culturist finds 

 it so difficult to procure suitable diet for his small charges. 



Around our coasts are distributed various kinds of sea-weeds, thus 

 where the bottom is rocky we find brown algEe (Fuci), and further out the 

 red form (Floridi). But, as already observed, with increasing depth 

 vegetation becomes less, or should sea-weeds drift to sea, they subside and 

 constitute soft black mud, wherein worms, molluscs, crustaceans and other 

 marine animals have their home and find their subsistence, while they in 

 turn form food for fish. Professor Mobius (Die Nahrung der Seetiere) at 

 90 to 95 fathoms in the Baltic, where the bottom consisted of plastic clay, 

 found very few worms : in the Mediterranean, south-east of Sicily, at 

 1700 fathoms, where the bottom consists of yellowish clay, the British 

 exploring expedition found no traces of animal life. But in the southern 

 parts of the North Sea, at 20 to 25 fathoms, and with a muddy bottom, such 

 is found to be alive with small crustaceans, worms, snails, molluscs, 

 and echinoderms, and as a result with fish which live there and prey 

 upon them. Irrespective of the foregoing vegetable substances, floating 

 sea alga?, which form food to marine animals, and sometimes micro- 

 scopic forms are so numerous as to render the surface almost turbid. 

 Diatoms live in every sea, and are consumed by pelagic animals, as Salpaa and 

 Pteropods. Likewise all rivers carry organic matter into the ocean, rendering 

 the bottom rich and a resort for the invertebrate animals, as well as the fish 

 which prey upon them ; while currents which carry plants and small marine 

 creatures from place to place must likewise influence the migration of fishes. 

 In short, the temperature, saltness, purity of the water, currents and depth 

 of the sea must each and all exercise a great influence upon animal and 

 vegetable life, also the character of the neighbouring shore, as regards its 

 geological formation and whether fertile or barren, rocky or sandy, and the 

 amount of surface drainage which flows into it. 



The food consumed by fresh-water forms has been more closely inves- 

 tigated than among marine species, and it is only by knowledge of what 

 is required, combined with care and constant attention in carrying such out, 

 that private fish-pond culture can be made profitable. Leaving them 



