メジナ

The life history of Girella punctata (Girellidae) was studied at the northern coast of Fukuoka from 1975 to 1977. As the subjects of this study, 0^+ and 1^+ age fishes of less than about 150 mm in BL were mainly investigated. To clarify the life history of this species, as to the morphological characters, number of fin rays and gill rakers, relative growth of head length, body depth, caudul peduncle depth and intestine length to BL, and forms of stomach and intestines were examined. Furthermore, ecological characters such as habitat and food habits were examined. As a result, all specimens less than about 150 mm in BL were graduated with the characters mentioned above into the following five developmental stages. Postlarval stage (3.7-15 mm BL) Body form is much more slender than that of adult. Each fin develops and fin rays attain their fixed number at about 15 mm in BL. Number of gill rakers increases rapidly. Stomach is straight and intestines are simple in a form. Living at the surface layer of coastal waters from May to mid-June, they feed on pelagic copepods and phyllopods. Prejuvenile stage (15-20 mm BL) Body form is still slender. Number of gill rakers increases as before. Stomach is L shaped, and forming bends, intestine increase in length. The habitat changes to the surface of rocky shores, and individuals feed on planktonic and benthonic copepods, phyllopods and amphipods. Postjuvenile stage (20-30 mm BL) Body depth becomes larger to some degree. Proportion of head length to BL attains maximum and that of caudal peduncle depth becomes constant at about 20 mm in BL. Scales cover most of the body at about 25 mm in BL Stomach is V shaped as in adults. Intestines enfold stomach passing under it from right to left and intestine length noticeably increases. Living in almost the same habitat as prejuvenile, they begin to peck at food organisms on the rocks, and sessile diatoms occur in their stomach contents as one of the main food organisms. Young stage (30-50 mm BL) Body form and coloration begin to resemble that adults. Number of gill rakers become nearly constant at about 30 mm in BL. Shifting their habitat from the surface layer to the middle and bottom layers on rocky shores gradually from late-June to late-July, they mainly feed on copepods, amphipods, schizopods, sessile diatoms and algae. Immature stage (50 mm BL -) Proportion of body depth to BL becomes constant at about 50 mm in BL and external appearance is almost the same as that of adults. Development of intestinal convolution finishes and proportion of intestine length to BL becomes constant at about 50 mm in BL. After August at 0^+ age, they feed mainly on sessile diatoms and algae, except in April and May when the 1^+ age fishes feed predominantly on amphipods and annelids.