Toru Taniuchi

Juvenile and small fishes in a mangrove estuary in Trang province, Thailand: seasonal and habitat differences

Abstract Juvenile and small resident fish assemblages at three sites (beach with mangroves, beach without mangroves and middle reach of mangrove creek), comprising the major habitat types of a mangrove estuary in Trang Province, Thailand, were studied for 3 years. A total of 6616 individuals, comprising 89 species (30 families), were collected using a small seine net. In terms of number of species per family, Gobiidae (18 species) was the most diverse, followed by Engraulidae (nine species) and Leiognathidae (seven species). In terms of individuals, Engraulidae, Leiognathidae, Gerreidae, Atherinidae and Gobiidae were the dominant families. Species richness was significantly greater in the mangrove creek than at the two beach sites, and greater in the wet season than the dry season. Fish abundance (individuals per tow) was also greater in the wet season, with no significant differences among sites. On the other hand, biomass (weight per tow) was greater in the mangrove creek than the mangrove beach, but with no significant difference between seasons. Cluster and ordination analysis based on the number of individuals of each species demonstrated that the fish assemblage structures were markedly different between the beach and creek sites, the assemblages at the two beach sites being similar in the wet season. Most species were specific to a particular habitat type (or types), some occurring exclusively in the creek or beach sites, and some in both the mangrove sites. Such distributional differences were found even between species within a single family. The results indicated that creek and beach habitats function as nursery sites for different fish species, the former being utilized by a grater diversity of species than the latter.

Geographic variations in reproductive parameters of the starspotted dogfish, Mustelus manazo, from five localities in Japan and in Taiwan

Geographic variations in reproductive parameters of Mustelus manazo from five localities, four in Japan (Aomori, Tokyo Bay, Maizuru, and Shimonoseki) and one in Taiwan, were investigated from November 1994 to June 1996. Differences in age and length at sexual maturity from Aomori to Taiwan were approximately 3 years and 300 mm in TL, respectively, for both sexes. The sharks appeared to mature at a later age and to a larger size in the most northern population, Aomori, and to be faster and smaller in the southern population, Taiwan. Mating, ovulation and fertilization periods were generally during May and August in the four localities of Tokyo Bay, Maizuru, Shimonoseki, and Taiwan. In Aomori, males showed no clear monthly variation in gonad index, and females in Aomori had a protracted reproductive period. Females became pregnant every year in all localities, except Aomori. The Aomori population apparently has a different reproductive cycle. The Tokyo Bay population is distinctive regarding growth and sex ratios of embryos. In all localities, the number of embryos per litter increased relative to total length of mother. There was no geographic variation in reproductive parameters between Maizuru and Shimonoseki. The coast between these last two sampling areas is a continuous steep slope with similar environmental conditions, and mixing of the two populations may occur.

銚子産ホシザメの年齢,成長,繁殖および食性について

Over 400 specimens of Mustelus manazo were collected from Choshi to study its age, growth, reproduction, and food habits. Annuli were estimated to occur on vertebral centra yearly from analysis of monthly marginal growth ratios. Linear relations were obtained between radius of centrum and total body length. Von Bertalanffy growth equations are described as follows; male: lt=l043[l-exp{-0.19 (t+2.00)}]: female: lt=277l[l-exp{-0.032(t+4.77)}]. Both males and females reached their first maturity at 621-640mm and all the specimens over 700mm attained their maturity. However, age determination suggests that females reached maturity at a little older age than males. Monthly gonad indices of males show that copulation occurred between June and July. Gestation period is estimated to be approximately 10 months. Litter size ranged from 1 to 22 with an average of 4.9, although litter size increased with the length of the parent. Stomach content analysis shows that Crustacea were the most important prey animals with 85% occurrence. Among others, percentage occurrence of crabs exceeded 50%. Fishes composed chiefly of sardine were also important food items as well as Polychaeta and Spinculoidea.

Filial Cannibalism in the Paternal Mouthbrooding Cardinalfish Apogon lineatus: Egg Production by the Female as the Nutrition Source for the Mouthbrooding Male

We investigated about filial cannibalism by Apogon lineatus based on 25 mouthbrooding males sampled in Tokyo Bay, Japan. Eggs were found in the stomachs of all mouthbrooding males, indicating that Apogon lineatus performs partial brood cannibalism. The number of eggs in the stomachs ranged from 1015 to 9384, corresponding to 30% on average of the entire brood. This study revealed that mouthbrooding males could gain considerable energy by partial brood cannibalism during brood periods, that is, females would produce surplus eggs as the nutrition sources for starving males.

Effects of changes in leaf height and shoot density on the abundance of two fishes,Rudarius ercodes andAcentrogobius pflaumii, in azostera bed

The effects of changes in the structural complexity of a seagrass habitat on the densities of filefish (Rudarius ercodes) and streaked gobies (Acentrogobius pflaumii), were investigated by conducting a 9 month field experiment in aZostera marina bed at Moroiso Bay, Aburatsubo, central Japan. The experimental design included a control and 7 treatments where leaf height or shoot densities were reduced. During the period of high density of filefish, the species was more abundant in quadrats with longer leaves and denser shoots, but this tendency was not observed during the period of low density. Filefish did not frequent the quadrat cleared of seagrass or the area of sandy substratum surrounding the experimental seagrass bed at any time. The abundance of streaked gobies did not differ significantly among 8 experimental quadrats, although the species seldom appeared over the surrounding sandy substratum. The results suggested that filefish, unlike gobies, were attracted to factors associated with theZostera leaves, such as epiphytic prey and/or the complex living space.

Occurrence of two species of stingrays of the genusDasyatis (Chondrichthyes) in the Sanaga Basin, Cameroun

SynopsisTwo species of the genusDasyatis were collected in the lower Sanaga Basin in the vicinity of Edéa, Cameroun, West Africa, during a survey from November 1985 to January 1986. Of these specimens, 34 were identified asD. garouaensis and one asD. ukpam. Thirty-one specimens ofD. garouaensis and oneD. ukpam were caught in the lower reaches of the Sanaga River while three were taken at the junction between the Nyong River and the channel connecting the two rivers. The distribution pattern of the two species is discussed.

Galeus longirostris, a new species of the sawtail catshark from Japan

Galeus longirostris sp. nov. is described based on 46 specimens taken off the southern part of Japan. It is distinguished from all known species ofGaleus in having a considerably longer snout. This species is morphologically close toG. nipponensis, which commonly occurs off the southern part of Japan, but differs in having longer preoral length than the mouth width, a bluntly rounded snout, larger pectoral fins, a shorter interspace between anal and lower caudal fins, and a greater number of monospondylous vertebrae.