eggs from adults exposed to 0.51 yg/liter was reduced slightly, and 0.22 

 and 0.51 yg/liter of toxaphene increased the mortality of fry and decreased 

 their growth. Toxaphene residues in fry from these two exposures were 8 

 and 32 ug/g, respectively. 



Toxaphene may also have an adverse effect on important natural fish 

 foods. Concentrations of 10 yg/liter or greater inhibited emergence of 

 midge larvae, but this is well above the concentrations affecting repro- 

 duction or growth in fish. However, greater resistance of midge larvae 

 could enable them to accumulate significant residues. Reproduction of 

 daphnids was halved when the organisms were exposed to 0.12 ug/liter toxa- 

 phene for 21 days, and the no-effect concentration was only 0.007 yg/liter. 



Toxaphene concentrations of 0.04 - 0.25 yg/liter are detrimental to the 

 production of fish and their food; consequently contamination of waters 

 supporting these resources by run-off, leaching, or spraying should be 

 avoided. Unfortunately, these low concentrations are very difficult to 

 detect analytically. However, tissue residues exceeding 0.4 - 1.8 yg/g in 

 salmonids may be associated with reduced growth and reproductive success, 

 and residues over 5 yg/g may cause reduction in growth of channel catfish 

 fry. 



Biochemical effects —Collagen is the major fibrous protein of all verte- 

 brates and serves as the major component in the organic matrix of connec- 

 tive tissue and bone. The proper ratio of collagen and minerals is 

 essential for rigidity and flexibility of bone, as well as overall develop- 

 ment and maturation. 



Eggs and fry of brook trout and young fathead minnows were exposed to 

 toxaphene for 90 and 1500 days, respectively, at the same concentrations 

 (0.039 - 0.5 yg/liter and 0.06 - 1.2 yg/liter) as those tested in the 

 growth and reproduction studies reported above. Analyses of backbones 

 showed that synthesis of hydroxyproline, the major amino acid of collagen, 

 was inhibited during the first few weeks of exposure to toxaphene at con- 

 centrations of 0.039 yg/liter or higher. In older fish collagen synthesis 

 was reduced at all concentrations of toxaphene by the end of the exposure 

 period and appeared to be correlated with reduced growth. The earliest in- 

 hibition of collagen synthesis occurred at the highest toxaphene concentra- 

 tions and preceded observable reductions in growth. 



In general, the net effect of toxaphene in fish was lower collagen 

 synthesis and greater mineralization of the backbone and whole body. We 

 postulated that this condition may cause the backbone of fish to be brittle 

 and fragile and therefore subject to breakage during times of swimming 

 stress. We subjected groups of toxaphene-treated and control fathead 

 minnows to a sublethal electrical shock (60, AC) and then examined the 

 backbones by x-ray. The observations (Figure 3) confirm that the backbones 

 of toxaphene-treated fish seem more fragile and could break while the fish 

 are migrating or escaping predators. 



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