of oil spills could similarly provoke these effects, which would almost 

 invariably be lethal to the egg. Cytotoxicity, mutagenicity, and less direct 

 physiological effects on the chromosomes and nuclei of the early-stage eggs 

 ought to depress the rate of their cell and chromosome divisions. 



In light of these findings and in response to the oil spill, an effort 

 was undertaken to determine the cytogenetic effects of oil on fish eggs. 



Microscopic examinations were made of the dissected embryos of 79 cod 

 eggs and 153 pollock eggs sampled in the vicinity of the Argo Merchant oil 

 spill. This was done using a new application of cytogenetic methodology to 

 fixed fish eggs from field plankton samples (Longwell, 1976). Similarly 

 examined were 75 cod embryos from eggs spawned in an aquarium by a small 

 number of females captured in the field. 



Sample size and station numbers are drastically limiting, and pollock 

 eggs were not represented in the sub-sample from Station 4. Even so, a 

 higher mortality of pollock over cod eggs is obvious. Totaled over all 

 stations, about 20% of the collected cod eggs were dead or cytologically 

 moribund as compared with 46% of the pollock eggs. For comparison, only 4% 

 of the sample of cod eggs spawned in the laboratory were dead or moribund 

 (Table 4-3) . The earlier developmental stages of the cod eggs studied should 

 have been more sensitive than the pollock eggs because natural mortality 

 rates are highest in younger embryos. Thus, any real difference between the 

 viability of cod and pollock eggs may be even greater than the numbers alone 

 indicate. 



At Station 8 the pollock embryos were malformed in 18% of the eggs; at 

 Station 9, in 9% of the eggs. Pollock eggs at Station 9 carry the strongest 

 implications for an adverse effect of the oil. Here mortality and moribundity 

 was 98% for a reasonable sample size (43 eggs) . About 60% of these eggs had 

 strikingly abnormal cell patterns. The large size of the cells of these 

 embryos can be interpreted as indicating that the influencing factor acted 

 much earlier in embryo development than the tail-bud and tail-free stages at 

 which the abnormal pattern was observed. In these embryos, chromosome and 

 cell division had almost entirely ceased or was blocked at the prometaphase 

 division of mitosis (a common action of chemical adversely affecting the 

 chromosome apparatus) . Almost all the rest of the pollock embryos at this 

 station were merely degenerating examples of this type of abnormal embryo 

 (Table 4-4). 



Oil adhered to almost all the pollock eggs from Station 9 (Figure 4-7), 

 and the amount of oil on individual eggs was also greater than at the other 

 stations. At this same station, fewer cod eggs were contaminated and the 

 individual eggs were not as heavily contaminated as the pollock eggs. The 

 reasons for the differential contamination are unclear. The pollock eggs 

 were at a later developmental stage than the cod eggs and may have been 

 sampled higher in the water column than the earlier stage cod, thus increas- 

 ing their chance of being contaminated with oil particles. The fixation of 

 the eggs may affect the adherence of oil to the egg membranes. The membrane 

 contamination observed in the fixed eggs is certainly real, however, sug- 

 gesting the possibility of species differences in membrance fouling. Normal 



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