A NEW PRINCIPLE OF AQUICULTURE. 763 



piece of scrim which formed the bottom of a box about 6 inches deep floated on 

 the top of the water in a protected pool. The eggs of Menidia and Fundulus 

 are hatched successfully by practically the same treatment. 



ADAPTATION TO FISHES AND OTHER PELAGIC FORMS. 

 REQUIREMENTS. 



In the development of the method of fish culture with which our station 

 is identified the installation of a laboratory directly upon the water and the 

 confining and rearing of animals in cars placed in the water marked the first 

 step. For many animals of the types we have mentioned, the slow moving, 

 or creeping, the burrowing, and the sessile animals, this is all that is necessary 

 for rapid and healthy growth. For pelagic animals, however, like the young 

 of most fishes and the larval forms of Crustacea and other marine invertebrates, 

 it is not sufficient. The very peculiarities of structure and instinct which adapt 

 these creatures to their pelagic life make it difficult to confine them for a long 

 time even in relatively large inclosures of the water in which they normally live. 



One is baffled now by one peculiarity and now by another. The larvse 

 or fry are often strongly heliotropic, and in going toward or away from the 

 light soon strike the boundary wall of their confine, and when they are numerous, 

 as they must be in practical culture, die from the effects of crowding, if, indeed, 

 they are spared to this fate by their cannibalistic comrades. Often in the 

 blind struggle to go toward the light regardless of the boundary wall, they grad- 

 ually work their way to the bottom and become entangled in debris or covered 

 with silt. 



If, for the sake of good circulation of water, the tidal current is allowed to 

 pass through the car, as in the case of sessile or bottom-living forms, the pelagic 

 fry are apt to be swept against one side, or to collect in eddies, with disastrous 

 results. If, on the other hand, the current through the inclosure is not supplied, 

 the water becomes stagnant and not well aerated, and since the time required 

 to rear most animals to a considerable size is long, the stagnation under these 

 circumstances is almost inevitable. 



The minuteness of many larval animals constitutes a fourth difficulty, for 

 perforations or meshes large enough to permit sufficient circulation frequently 

 permit also the escape of the fry, while meshes too small for the fry to go through 

 become clogged with silt and do not allow free circulation. 



The fifth difficulty in the rearing of pelagic fry in inclosures of this kind 

 depends upon the fact that normally they capture their prey "on the fly." 

 A dilemma presents itself: If the fry are fed upon smaller animals or plants, 

 these too must be pelagic, involving all the difficulties over again, while, if 

 artificial food is used, there is no provision for keeping it in suspension, in which 

 condition only would it be available. 



