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.
Early life history of the threebanded sweetlip, Plectorhynchus cinctus was studied from eggs, larvae and juveniles reared in the laboratory.Juveniles collected from the Suo Sea in the western region of the Seto Inland Sea were also studied.The artificial insemination was carried out in June and July and larvae were reared from June 25 to September 7 of 1981. Eggs were 0.79 mm in diameter, pelagic, spherical with a single oil globule of 0.20 mm in diameter.Incubation time was 33-35.5 hours at the temperatures of 21.6-23.2°C.Length of prolarva 2 hours after hatching was 2.2 mm.By the time of yolk absorption in three days larvae grew to 2.9 mm.Transformation of larvae to the juvenile stage was completed at 9.1 mm.During early developmental stages, outstanding features included the formation of head armatures and dense pigmentation of body.Head armatures were acquired in the sequence of preopercular spines at 3.3 mm, supraorbital and upper cleithral spines at 5.5 mm, and postocular and subopercular spines at 9.1 mm.Several of these spines and the conical teeth in early juveniles were lost in the advanced specimen of 21.3 mm.In advanced larvae and juveniles melanophores were scattered over the entire surface of body except the upper parts of soft dorsal and anal fins, pectoral fin and caudal fin including caudal peduncle.This color pattern changed rapidly by physical stimuli from the uniformly black to the pale with distinct four oblique bands suggesting the potential differentiation of the typical color pattern in this species.A wild-caught juvenile, 50 mm in total length was provided with three oblique bands and several dots which were more distinct and fewer than those in the adults.In the fields, juveniles were found from early July to early August in the surf zone in the waters surveyed.
Three hundred and ninety five specimens of Gasterosteus aculeatus microcephalus were collected from the Yamayoke River and Tsuya River in the southwestern part of Gifu Prefecture and the Amano River in the northeastern part of Shiga Prefecture, Japan.Their morphometric and meristic characters were examined to study whether or not this species shows sexual dimorphism. The number of anal fin rays showed a tendency to be larger in males than in females.Another marked sexual difference was found in the ratio of the head length to the body length: the pro-portional head length was clearly larger in males than in females.This dimorphism seemed to have occurred in relation to breeding habits.Males frequently use the head in fighting to guard their territory and in building nests.The larger head of males may make easy to do so.The ethological significance of the larger head of male is discussed.
The present paper deals with ovarian maturation by hormone injection and morphological development of the amberjack, Seriola aureovittata Temminck et Schlegel.Ovarian maturation of the amberjack during the spawning season was successfully induced by injection of either “Gonatropin7” (Teikoku Zoki Mfg.Co.Ltd.), or Hypophthalmichthys molitix's pituitary homogenate, or H.molitrix's pituitary homogenate combined with “Gonatropin”.The last dosage was evaluated to be the most effective and reliable.The spawning period seemed to ex-tend from late April to the mid-May in the Sea of the Goto Islands.On May 14, 1977 the authors performed artificial fertilization of the specimens which were artificially induced to mature by the hormone injection, and reared the hatched larvae to grow to the juvenile stage.The eggs of the amberjack are pelagic, spherical in shape and 1.27-1.50mm in diameter.The yolk is roughly segmented and contains a single colorless oil globule of 0.34-0.36mm in diameter.The perivitelline space is narrow.During embryonic development, many melanophores and xantho-phores appear on the embryo and oil globule.Hatching took place in 96 hours after artificial fertilization at water temperatures between 15.5 and 20.4°C.The newly hatched larvae were 4.45-4.55mm TL and had 26 (12+14) myomeres.Characteristic features at the larvae were that the oil globule was situated at the anterior part of the segmented yolk which was extended slightly beyond the head and that the granules existed on the marginal fin which was densely pigmented with xanthophores.The yolk was almost all absorbed when the larvae attained 5.23-5.45mm TL, 4 days after hatching.In a 9-day old postlarva, 6.25mm TL, small denticles appeared on the margin of the upper jaw and there were 4 opercular spines on the preoperculum.In a postlarva 19-days after hatching, 7.5mm TL, the notochord was turned up and caudal, dorsal and anal fins with rudiments of rays were beginning to develop.In a 30-day old juvenile, 15mm TL, the coloration of the body was pale greyish black with the characteristic 2 yellow bands situated at the anterior part of the trunk and the caudal region.In a juvenile of 40-days, 23mm TL, 3 4 greenish dark brown cross bands appeared on the posterior part of the side of the body.The number of the bands increased to 7 at a size of 45mm TL, but such bands had disappeared in a specimen of 195mm TL.
In Nagasaki Prefecture during 1981, larvae and juveniles of Allanetta bleekeri were collected from June to October with a larva net and dip net in Omura Bay, and immature individuals were collected under fish lamps in Nomo Harbor from April to December.Morphological development, local occurrence and food composition, especially in larval and juvenile stages, were studied. A.bleekeri reaches the juvenile stage at sizes of 13.2-15.6mm in total length.The common morphological characteristics of other species of the Atherinidae were observed in larvae and juveniles.These include round head, short trunk, long and compressed tail, melanophore procession along the dorsal edge of the body, longitudinal black stripe formed laterally, fin fold remaining till early juvenile stage.The following points are important to distinguish larvae and juveniles of A.bleekeri from those of the other species of the same family, due to their supposedly sympatric occurrence: presence of melanophores on rear of notochord and caudal fin base, presence of ventral melanophore procession between pelvic and anal fins, and reach of lateral stripe.Relative growth during the early developmental stages is divided into three phases: larval, juvenile (up to 20-25mm in total length), and ault-form stage. Larvae were collected with a larva net from the surface layer.They occurred abundantly from June to early September along the coast where Zostera marina or Sargassum spp.grew thick.Their occurrence is thought to have started in May.Larva net collection showed rather extensive distribution in the young larval stage.Well-grown larvae and juveniles were observed to form concentrated schools along the sea-wall of a harbor in September and October. Investigation on food composition in digestive tracts revealed A.bleekeri to be a zoo-plankton feeder mainly relying on Copepoda and its larvae.
西海区水産研究所の沖縄舟状海盆トロール調査において, 6対の鰐孔を持つエイが採集された。この標本はChu and Meng in Zhu et al. (1981) が南シナ海から報告した1科1属1種のHexatrmatobatis longirostrumの記載によく一致するので, この種に同定し, 和名をムツエラエイとした.本種はHeemstra and Smith (1980) が南アフリカから報告した1科1属1種のHexatrygon bickelliと酷似しており, genus Hexatrematobatisはgenus Hexatrygonのjunlor synonymと考えられる、両種は吻部の形状によって区別される。 Heemstra and Smith (1980) はH.bickelliの鰓孔が6対あること, 噴水孔が眼球よりずっと後方に位置すること, 吻部が前方に突出することなどの特化形質をもとに, Myliobatiformesトビエイ目, Hexatrygonoideiムツエラエイ亜目を提唱しているが, 著者らもこれに従う.