FISHERY BULLETIN: VOL 76, NO. 1 



ical disruption of tissues, no mechanism of 

 pathogenesis is apparent for nematodes in shrimp. 



NONINFECTIOUS DISEASES 



Toxic Responses 



In the last decade, because of interest in aquatic 

 pollution, some research has been done on toxic 

 responses of penaeid shrimps to a variety of chem- 

 icals and heavy metals. Most of this w^ork has been 

 done in pollution-oriented laboratories; however, 

 few attempts have been made to apply results to 

 interpretation of field conditions. Results obtained 

 have been reported mostly as toxicity of specific 

 chemical agents in terms of short-term lethality or 

 longer-term mortality. Unfortunately, little indi- 

 cative cellular or tissue changes caused by toxi- 

 cants has been described for penaeid shrimps. I 

 shall divide this section into categories of toxi- 

 cants that have been tested or studied in penaeids. 

 The following categories will be covered: or- 

 ganochlorines, organophosphates, carbamates, oil 

 or petroleum products, heavy metals, and chemo- 

 therapeutic chemicals. 



Organochlorines 



Since World War II many kinds of pesticides and 

 industrial chemicals containing or consisting of 

 chlorinated hydrocarbons have been inadver- 

 tently or intentionally released into the envi- 

 ronment. Aquatic life is exposed to these com- 

 pounds because the aquatic portion of the 

 biosphere often behaves as a "sink" or receptacle 

 for these compounds due to runoff or fallout. Some 



Table 4. — Comparative toxicity of pesticides to three estuarine 

 taxa — most sensitive (1) to least sensitive (3).' 



' This table was prepared by Jack I. Lowe who graciously granted permission 

 for Its use here The table has not been published previously 



of these compounds or their metabolites are re- 

 fractory to breakdown, and thus tend to accumu- 

 late in various compartments of the aquatic envi- 

 ronment. Experimental shrimp have been found 

 to accumulate certain chlorinated compounds in 

 the laboratory and feral shrimp have possessed 

 detectable levels when taken directly from con- 

 taminated or apparently "clean" waters. Jack 

 Lowe of the USEPA Laboratory, Gulf Breeze, has 

 found, over several years of testing, that penaeid 

 shrimps generally are far more sensitive to toxic 

 effects of most insecticides than are fishes or mol- 

 lusks (Table 4). The effects of some of the better 

 known compounds will be reviewed here. 



DDT 



White shrimp, which died as a result of DDT 

 exposure, accumulated up to 40.40 ppm DDT and 

 DDE in hepatopancreas after 18 days exposure to 

 0.20 ppb in flowing seawater (Nimmo et al. 1970). 

 Exposure to DDT concentrations greater than 0.10 

 ppb was lethal to pink shrimp in 28 days. A 

 physiological effect of DDT exposure in pink and 

 brown shrimps was loss of certain cations in the 

 hepatopancreas (Nimmo and Blackman 1972). 

 Sodium and potassium concentrations in shrimp 

 exposed to 0.05 ppb DDT for 20 days were lower 

 than in those not exposed. Magnesium, however, 

 was not significantly lowered. The significance of 

 reduced cations in the hepatopancreas of shrimp 

 for the pathophysiological behavior of shrimp is 

 not known. Blood protein levels also have been 

 found to drop in shrimp exposed to DDT. There are 

 no reports of histopathological changes in 

 penaeids following exposure to DDT. In acute, 

 high-concentration exposures, shrimp showed 

 tremors, hyperkinetic behavior, and paralysis, 

 classic signs of DDT poisoning in arthropods. After 

 extended exposure to low concentrations of DDT, 

 shrimp did not become paralyzed, but sank into 

 lethargy, refused food, and then died. 



Dieldrin 



Pink shrimp were more sensitive to dieldrin 

 than were grass shrimp in test exposures. How- 

 ever, both species died when exposed to concentra- 

 tions of dieldrin in the low parts-per-billion range. 

 Pink shrimp had a 96-h LC^y of 0.9 ppb dieldrin 

 (Parrish et al. 1973). No histopathological effects 

 of dieldrin in penaeid shrimps have been re- 

 ported. 



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