Estimation of larval stage determining the appearance of albinism in hatchery-reared juvenile flounder Paralichthys olivaceus.

Abstract

The larval stage of the flounder P. olivaceus, when their body color (normal coloration or albinism of juveniles) was determined, was estimated by two ways of feeding. One was to feed Brazilian Artemia nauplii and rotifers which induce albinism easily in a high percentage. The other was to feed wild zooplankton and rotifers which usually induce normal coloration in a high percentage. Larvae of 10 days old were divided into 8 lots of 1, 000 larvae each and were fed for 29-30 days on different feeding schedules at different growth stages by a combination of the 2 feeding methods. Based upon the percentage of normal coloration and albinism at the end of experiment, 8 experimental lots were divided into 3 groups. In the first group (Tanks 1-3) in which Artemia nauplii were changed to wild zooplankton before the larvae grew up to D stage, the highest percentage of normal coloration was observed (60.2-75.4%). In the third group (Tanks 5-8) fish began to accept wild zooplankton from E stage, the highest percentage of albinism was ob-served (90.9-100.0%). In the second group (Tank 4 only), wild zooplankton were given to larvae in place of Artemia nauplii when the larval developmental stages consisted of 25% D and 75% E, and this composition agreed well with the percentage occurrences of normal coloration (27%) and albinism (73%). From these results, D stage was estimated to be the critical stage deter-mining the juvenile's coloration in terms of kinds of live foods.