DIRECT FEMINIZATION OF LUMPFISH (CYCLOPTERUS-LUMPUS L) USING 17-BETA-ESTRADIOL-ENRICHED ARTEMIA AS FOOD

Artemia nauplii cultured in lipid-enriched media containing 0, 5, 10 o r 20 mg 17beta-oestradiol/l for 24 h.contained 0, 140, 90 and 231 ng 1 7beta-oestradiol/mg dry wt., respectively. Feminization of lumpfish la rvae was essentially 100% when the larvae were fed Artemia containing 231-407 ng 17beta-oestradiol/mg dry wt. at first feeding for 20 days. Immersing eggs or newly hatched larvae at 22, 29 and 36 days post-fert ilization in 200 mug 17beta-oestradiol/l for 2 h resulted in 68% and 4 6% females in duplicate treatments. The ovaries of some fish which con sumed Artemia containing 17beta-oestradiol were smaller, filiform and less developed than those from similar size control females although n o spermatogenic tissue was detected in these filiform ovaries. This ma y indicate that females with filiform ovaries were feminized, genotypi c males. It appears that direct sex-reversal techniques, based upon st eroid-supplemented Artemia nauplii, has promise of producing monosex p opulations in fish larvae requiring a diet of live prey during the per iod of sex determination.