96 



JAMES W. ATZ 



About 50 years ago, artificial fertiliza- 

 tion and incubation of the eggs of marine 

 food fishes were carried out on a large 

 scale in order to replenish defining natural 

 stocks (e.g. see papers presented at the 

 Fourth International Fishery Congress, 

 Washington, 1908, which were published 

 in 1910 in vol. 28 of the Bulletin of the 

 U.S. Bureau of Fisheries) . A critical look 

 at the biostatistics involved (e.g. by 

 Breder, 1922) demonstrated the useless- 

 ness of the procedure, which was even- 

 tually abandoned. Little systematic effort 

 was made to rear the fish, since they were 

 released or planted shortly after hatching, 

 and Morris (1956) found that few" data 

 helpful for laboratory culture had been 

 recorded. 



Hertling (1932) and Morris (1956) give 

 accounts of some of the early attempts to 

 rear marine fishes from the egg. Much 

 of the difficulty encountered was referred 

 to the so-called critical period, when the 

 larva, having used up its yolk supply, be- 

 comes dependent on other, external sources 

 of food. While recognizing the radical 

 nature of this vital change in larval nutri- 

 tion, Morris makes it clear that in some 

 species this is not an especially critical pe- 

 riod, in the sense that no greater mortality 

 is suffered at the time of the change. 

 Marr (1956) reviews the evidence for a 

 critical period in nature and concludes 

 that it is not well demonstrated. Well 

 taken is the point made by Morris that 

 until the sensitivity of any given species 

 has been determined, "the situation can be 

 considered critical from the time of fer- 

 tilization until organogenesis is com- 

 pleted." 



Because of the rigid requirements of the 

 eggs and larvae of marine fishes, data de- 

 limiting their tolerance of environmental 

 factors and establisliing optima should be 

 especially useful. The series of papers by 

 Bishai (1960a, 1960b, 1960c, 1961a, 1961b), 

 supplemented by Holliday and Blaxter 



(1960) and Blaxter (1960), provides a 

 convenient and comprehensive summarj^ 

 of this autecological approach. A point 

 to be remembered, however, is that the lim- 

 its of tolerance of eggs and larvae for con- 

 ditions in captivity are often less than 

 those exhibited in the wild, probably be- 

 cause of the generally suboptimal artificial 

 environment. Moreover, not all of the 

 environmental factors affecting fish larvae 

 in nature have been studied. For example, 

 attention has recently been directed to pos- 

 sible lethal effects of light (Perlmutter, 

 1961), and this element should be given 

 consideration by the experimentalist. 



The extreme sensitivity of fish larvae in 

 general, and of those of marine species in 

 particular, to substances in the water sur- 

 rounding them is well recognized. Con- 

 tainers made of chemically inert materials 

 such as glass and certain plastics must be 

 used, preferably those that have never 

 been in contact with formaldehyde, clean- 

 ing solution, and the like (Morris, 1956; 

 Costello et al., 1957). It is now feasible 

 to construct a small yet efficient circula- 

 tory system entirely of nonmetallic ma- 

 terials — a vital piece of laboratory equip- 

 ment that remained an impractical ideal 

 for many years. A satisfactory formula 

 for artificial sea water in which fish larvae 

 have thrived has yet to be developed, while 

 MacGinitie (1947) has pointed out that 

 natural sea water "rots on standing, and 

 the resulting chemical and pH changes are 

 lethal, particularly to larval forms."' 

 These changes are undoubtedly the result 

 of the tremendous multiplication of bac- 

 teria in stored sea w^ater ; they may be con- 

 trolled with antibiotics (Oppenheimer, 

 1955; Marshall and Orr, 1958; Rustad, 

 1960; Shelbourne, 1963a) or ultraviolet 

 radiation (Wood, 1961 ; Herald et al., 

 1962), but cleanliness, aeration, filtration, 

 and storage in the dark remain the princi- 

 pal means of maintaining sea water in a 



