An Estuarine Low-Temperature Fish-Kill in Mississippi, with Remarks on Restricted Necropsies

Abstract

In January 1973, large numbers ofMugil cephalus (striped mullet), w eighing approxi- mately 250 gmeach, died in tw ofreshw aterlocalities in tidew aterbayous ofJackson C ounty, M is s is s ippi. Fis h identified as Mugil curema,M. cephalus, Megalops atlantica,Dormitator macu- latus, and Fundulus grandis w ere found dead in other low s aline es tuarine areas . Fis h-kills during cold periods areless commonly encountered in M ississippithan in Texas orFlorida. This particular incidentis attributed toconditions ofs tres s forfis hes incompletely acclimated tothe encountered low temperatures. Themostdeleterious stress w as thelow salinew aterw hich prob- ably allow ed a breakdow n in the fishesÕion-osmoregulatory mechanisms. Striped mulletand othereuryhaline fishes in salinities greaterthan 6 pptsurvived,as did freshw atercentrarchids and ictalurids in areas w ith dying mullet. Otherstresses thoughttocontributetothew eak- e n in g of s t r ip e d m u l l e t in P a ig e B a y ou d u r in g t h e p e r iod of r a p id l y d e c r e a s in g t e m p e r a t u r e s in - clude s tarvation and high levels of pes ticide res idues . I n examined fis h, the alimentary tracts w ere devoid of fod, the gall bladders w ere dis tended and leaking bile, the livers contained e x c e s s l ip id m a t e r ia l a n d w e r e of t e n s t a in e d t h r ou g h ou t w it h b il e p ig m e n t s , a n d t h e l e v e l s of DDT metabolites and endrin res idues in the liver w ere higher than in control fis h. Stres s caus ed by low levels of dis s olved oxygen, toxic s ubs tances in the w ater, or dis eas e w as dis - c ou n t e d a s a c a u s e of d e a t h .