| Abstract
| - Organochlorine (OCs) and butyltin (BTs) residues weredetermined in mesopelagic myctophid fishes collected fromthe western North Pacific to elucidate contaminationstatus, accumulation patterns, and distribution. AmongOCs, concentrations of PCBs (polychlorinated biphenyls)and DDTs (DDT and its metabolites) were the highest inmyctophids (at maximum concentrations of 370 ng/gand 280 ng/g lipid wt, respectively). CHLs (chlordanecompounds) or HCHs (hexachlorocyclohexanes) were thenext most abundant OCs, and HCB (hexachlorobenzene)was the lowest. The maximum concentration of total butyltin(∑BTs = MBT + DBT + TBT) in fish was 46 ng/g wetwt. Concentrations of PCBs, CHLs, and BTs were significantlylower in oceanic myctophids than those in fishes fromJapanese coastal water, Suruga Bay. The residue patternof OCs and BTs showed a specific trend according todiel vertical migration of myctophids. Relatively highconcentrations of PCBs, DDTs, and CHLs were found innonmigratory species living in deeper waters, whereasconcentrations of HCHs, HCB, and BTs were high in migratoryspecies, which migrate up to the upper 200 m at nightfor feeding. These patterns are also influenced by thevertical distributions of OCs and BTs in the subarctic andtransitional waters of the western North Pacific, whereintrusion of watermass from the Okhotsk Sea has beensuggested. Temporal variation in the residue level andcomposition of OCs found in myctophids indicated a significantdecrease in the input of DDTs into the marine environmentwhile HCHs declined at a slower rate.
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