Measures of Bioeffects in Fish 



Micronuclei. Micronuclei are likely formed as a consequence of chromosome breakage or 

 spindle dysfunction during mitosis. Micronuclei occur at background levels in uncontaminated 

 conditions, but at very low incidences. Chromosomal aberrations and micronuclei may have 

 a role in evolutionary changes. However, elevated incidences of micronuclei above 

 background rates have been attributed to x-rays and specific chemicals with mutagenic 

 properties. Therefore, as applied in the context of monitoring marine pollution, this test can 

 be assumed to be responsive to chemicals with specific types of effects, primarily 

 genotoxicity. Although the degree of pollution-related elevation of micronuclei incidence 

 observed in studies of fish and mussels performed thus far are small, the differences between 

 contaminated and uncontaminated conditions are often significant and show a consistent 

 pattern among species. The background frequencies and the degree of elevations in 

 frequencies at sites that are contaminated does not appear to be species specific. 



Whereas the enzymatic indicators of effects may respond to toxicants in time scales of 

 days, micronuclei formation may be indicative and integrative of longer term exposures. The 

 lifetime of blood cells may be several months. In a mobile animal, such as P. stellatus the 

 measures of micronuclei abundance may be most useful when distinct populations are sampled 

 and compared. 



In this evaluation, mean total micronuclei incidence in peripheral erythrocytes in fish 

 caught in November-December ranged from 0.1 per 1,000 at RR to 2.4 per 1,000 at BK. The 

 highest incidences were among fish from the San Francisco Bay sites compared to fish from 

 coastal reference sites. In 27 New England coastal areas, micronucleus frequencies in mature 

 erythrocytes of winter flounder (Pseudopleuronectes atnericanus) ranged from 0.2 per 1,000 at a 

 site at Georges Banks to 5.6 per 1,000 at a site in Long Island Sound. The ratio of the 

 highest and lowest value indicated a 29-fold difference between sites (Table 40), similar to 

 that (24-fold) observed in the present study with P. stellatus. Overall mean frequencies in 

 the New York Bight Apex (2.33/1,000, n=39) and throughout Long Island Sound (3.94 per 

 1,000, n=35) were significantly higher than in offshore areas (e.g., 0.46 per 1,000, n=13 on the 

 mid-Atlantic shelf) (Longwell et al., 1983). 



Mean micronuclei frequencies in the cells of the gills of Mytilus galloprovincialis ranged 

 from 2.2 per 1,000 to 4.7 per 1,000 at six sites in the Venetian Lagoon, Italy (Brunetti et al., 

 1988). The highest frequencies were generally found in populations nearest sources of 

 pollutants. 



Mean micronuclei incidences in peripheral erythrocytes of Umbra limi injected with 

 ethyl methanesulphonate exceeded those in control fish (maximum of 3.71 per 1,000 vs. 0.14 

 per 1,000), however the test was not dose-responsive (Metcalfe, 1988), possibly due to toxic 

 effects on mitosis (Majone et al., 1987). Repeated injections of benzo(a)pyrene in Ictalurus 

 nebulosus resulted in a dose-responsive increase in peripheral erythrocyte micronuclei. 



White croaker (Genyonemus lineatus) caught in California coastal waters off Dana Point 

 had lower frequencies of micronuclei in peripheral erythrocytes (mean of 0.8 per 1,000, n=28) 

 than those caught in San Pedro Bay (mean of 3.5 per 1,000, n=28) (Hose et al, 1987). Similar 

 studies of kelp bass (Paralabrax clathratus) showed that fish from Catalina Island had lower 

 incidences (mean of 0.6 per 1,000, n=15) than fish caught off White Point near a major sewer 

 discharge (mean of 6.8 per 1,000, n=15). The ratios of the maximum and minimum values 

 observed in the studies of these two species was about 4.4- and 11.3-fold, respectively (Table 

 40), as compared to 24-fold for P. stellatus in the present study. Nuclear pleomorphism also 

 was found in those fish with the highest micronuclei frequencies. Though differences in 

 micronuclei frequencies between sites were significant for both species, micronuclei counts 

 were only weakly correlated with concentrations of tDDT and tPCB in the fish livers. 

 Highest frequencies, however, occurred in fish from areas known to have high concentrations 

 of PAHs in sediments. 



86 



