Early Life History of Lutjanus vitta (Lutjanidae) in Yuya Bay, the Sea of Japan

抄録

The morphology and ecology of Lutjanus vitta in early developmental stages were studied.Materials were collected with plankton nets, seines and trawls from 1975 through 1977 in Yuya Bay located in the southwestern part of the Sea of Japan.Larvae and early juveniles of the fish are outstanding in having an elongate second dorsal spine, pelvic spines, and pelvic rays.The body is compressed, and the head is armoured with spines and bony projections on the maxillary, posttemporal, supracleithrum, postcleithrum and four opercular bones.The fish attain full fin ray counts at about 10mm SL (= standard length) and specific coloration around 24mm SL.Relative growth of the elongate fin elements consists of four stanzas delimited by three growth inflexions which occur at about 7, 16 and 32mm SL.Close correlations between morphological and ecological changes were observed.Larvae less than 7mm SL spend planktonic life in the open sea, showing rapid growth in fin elements, adapting to the life mode.At about 7mm SL, a sharp downward inflexion occurs simultaneously in these fin elements, and the negative growth rate is maintainted until the fish measure about 16mm SL.In this growth stanza, the fish develop free-swimming ability gradually, migrate into bays and concentrate in shallow waters.In the third growth stanza (16-32mm SL), relative growth is highly negative (the relative growth coefficients, a<<1) in these body parts and actually negative (a<0) in some of them indicating a fast decrease of these parts in proportion to the length of the fish.In this growth stanza the fish move into grass beds, and the transition from pelagic to demersal life is completed at the end of the stanza.Over 32 mm SL, relative growth is slightly negative and stable until 20 cm SL, the size limit of the observations.Stomach contents of demersal young fish caught in grass bed were analyzed and a flexible feeding strategy was demonstrated.The fish is seemingly a random feeder which utilizes the most abundant food items available from more than one microhabitat within grass beds.They take small fishes and crustaceans both at the sea bottom, on Zostera blades, and in the water column between Zostera blades.