EVALUATION OF BALTIC HERRING AND ICELANDIC COD LIVER OIL FOR EMBRYO TOXICITY, USING THE JAPANESE MEDAKA (ORYZIAS-LATIPES) EMBRYO LARVAL ASSAY

These studies were carried out to determine if oils obtained from wild fish populations were contaminated with polychlorinated-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) and, if they were contaminated, would they result in embryo toxicity as measured by the Japanese medaka (Oryzias latipes) embryo larval bioassay (ELA). Three fish oils [Baltic herring oil (HO 1); Baltic herring oil spiked with 44 parts per trillion (pptr) of 1,2,3,7,8,9-HxCDD, 120 pptr OCDD and 130 pptr 2,3,7,8-TCDF (HO 2*); and a commercially available cod liver oil (CL)] and a corn oil sample were tested for embryo toxicity in a static renewal protocol. The ELA assay was selected due to its sensitivity to biological effects following dioxin and dibenzofuran exposure. Two of the fish oils (HO 1 and HO 2*) were from Baltic herring collected from the Gulf of Bothnia, Sweden, and the third was a commercially available Icelandic cod liver oil. The Baltic herring oil contained higher levels of both PCDDs and PCDFs than the cod liver oil: 2,3,7,8-TCDD, 5x; 1,2,3,7,8-PeCDD, 5x; 1,2,3,6,7,8-HxCDD, 6x; 2,3,7,8-TCDF, 3x; 1,2,3,7,8-PeCDF, 3x; 2,3,4,7,8-PeCDF, 4x; 1,2,3,4,7,8/1,2,3,4,7,9-HxCDF, 3x; 1,2,3,6,7,8-HxCDF, 4x; and 1,2,3,4,6,7,8-HpCDF, 2x. The HO 1 sample resulted in 30 to 90% death, whereas the HO 2* sample caused 100% death. The major lesions were hemorrhage, cardiac effects and tissue necrosis. The time to lesion occurrence and the types of lesions were similar to those observed in studies using pure 2,3,7,8-TCDD. The rearing solution control, corn oil control and cod liver oil samples caused no mortality or lesions. The lethality and lesions caused by these oils in the ELA system were similar to those reported in Salmo salter with the M74-syndrome from Sweden. The use of contaminated fish oils, therefore, may be one cause of poor viability in hatchery salmon reared in Sweden, and care should be taken when using naturally occurring fish or fish oils in nondefined feeds.