1+Oi^ 



EXPERIMENTAL FISH EMBRYOLOGY 



Injury or ablations of the embryonic shield and neural keel generally show localized 

 effects, particularly when they occur in the midline of the embryonic axis. After organ 

 differentiation, the damage tolerated must be only a small fraction (less than 10^) of the 

 available tissue. This applies particularly to the formed brain, sense organs, fin, tail, 

 etc. 



In all of this type of work it must be remembered that some of the results may be due 

 to incidental handling of the embryo, as in decapsulating. Also, it is somewhat more dif- 

 ficult to excise a specific region, and only that region, in fish than in the amphibian 

 (or even chick) embryos. Collateral injuries may be the primary cause of failure in re- 

 constitution. Operational skill with fish material Is achieved only with great patience, 

 persistence, and repetition. 



THE CULTURING OF FISH EXPLANTS IN VITRO 



This type of investigation, so readily achieved with amphibian and even with chick 

 material, proves satisfactory but to a lesser degree with fish embryonic parts. Oppen- 

 heimer (1958) cultured parts of Epiplatys fasciolatus in a modified Singer's for from 

 4 to 7 days and secured tail-like differentiation without histogenesis. 



Figs. 1 to 7. The types of differentiation attained in isolated blastoderms which have 



not gastrulated. These are hyperblastulae , masses of cells generally differentiating only 



a hollow vesicle whose wall represents the ectodermal portion of the yolk-sac epithelium. 



The stage at which the blastoderms were removed from the yolk, and the number of days they 



survived before preservation, are indicated in parentheses. Cell walls are represented 



only in Fig. 1. 



Fig. 1. Hyperblastula in which the non-differentiated embryonic cells form a compact mass 

 In the center of the vesicle. (16-celled; 4 days.) 



Fig. 2. Hyperblastula in which the non-differentiated mass of cells is continuous with the 

 vesicle epithelium at one region only and surrounded elsewhere by a columnar epi- 

 thelium. (32-celled; 3 days.) 



Fig. 3. Explant whose differentiated cells are joined to the vesicle epithelium by a 

 mesenchymatous network. (8-celled; 4 days.) 



Fig. 4. Explant In which the cellular arrangement suggests tlie occurrence of irregular 

 cell movements. Except for the formation of columnar epithelium no hlstogenlc 

 changes have taken place. TJie cell movements were not those of gastrulation. 

 (16-celled; 38 days.) 



Fig. 5. Hyperblastula containing two different types of cells, one non-differentiated, the 

 other with denser nuclei and more heavily staining cytoplasm (NV) . These probably 

 present cells which have commenced self-dlfferentlat Ion of nervous tissue without 

 the Inductive stimuli of gastrulation. (64- to 128-celled; 39 days.) 



Fig. 6. Hyperblastula in wliicli one group of cells has the dense nuclei characteristic of 

 nervous tissue (NV) , while another group (N) is surrounded by a heavy sheath simi- 

 lar to that normally surrounding the notocliord. These cell groups are large splierl- 

 cal masses, surrounded by homogeneously arranged non-differentiated cells; their 

 differentiation has been Independent. (2-celled; 3 days) 



Fig. 7, Hyperblastula in which a small group of cells, probably epidermal in origin, have 

 begun to self-differentiate nervous tissue (NV) . (8-celled; 6 days.) 



(From Oppenhelmer 1959: Jour. Exp. Zool. 72:21+5) 



