Malformations of the mouth shape, such as the“open-jaw syndrome”and“twisted lower jaw”, occur highly frequently in the ayu, Plecoglossus altivelis (Komada, 1974, 1980).It is also well known that the fish undergoes a change in the type of dentition on the jaws during the young stage (Matsui, 1938;Chapman, 1941;Iwai, 1956, 1962).In this paper, mouth shape, number and distribution of conical teeth in the juvenile stage, and period of shedding of the conical teeth and of formation of comb-like teeth on the jaws in young stage were described and reported to establish a basis for differentiating normal and ab-normal structures.The present study is based upon 800 specimens from Tanabe Bay, Wakayama Pref., and the Yahagi River, Aichi Pref., 400 specimens from Lake Biwa, 200 specimens from the Ado River, Shiga Pref., and 413 hatchery reared specimens, measuring 25-90 mm in standard length (SL). In the juvenile stage, 30-70mm SL, the lengths of the maxillary and the dentary and the width of the vomer in fish from Tanabe Bay were larger than those from Lake Biwa.The numbers of conical teeth on the vomer, palatine and dentary in fish from Lake Biwa were significantly larger than those from Tanabe Bay (t-test, p<0.001), and the number of these teeth in hatchery reared fish was clearly reduced.But there is no difference in number of conical teeth on the elossohval and mesopterygoid between these three samples. In 78 specimens (32.5%) of 240 hatchery reared fish, the lower jaw was twisted either to the right or left, and in 112 specimens (46.7%) the hyobranchial skeleton was ventrally projected.In these fish, the morphology of the vomer, palatine and dentary appeared normal, but the conical teeth on the bones were lacking at rates of 29.6%, 30.4% and 26.7%, respectively. The conical teeth on the vomer, palatine and dentary were worn away or lost in 50-60 mm SL fish from the Yahagi River.On the other hand, the conical teeth were done in 66-80 mm SL fish from Lake Biwa and the Ado River.The conical teeth were shed from the bones in 50-56 mm SL hatchery reared fish. In fish of 45-70 mm SL, the number of teeth groups on the outer surface of the jaws were significantly larger in fish from the Yahagi River than in those from Lake Biwa and the Ado River (t-test, p<0.001).But, there was no difference between the specimens from Lake Biwa and from the Ado River.In the same stage, the length of denticles in comb-like teeth on the upper jaw of fish from the Yahagi River were clearly larger than those from Lake Biwa and from the Ado River (t-test, p<0.001).There was no difference between fish from Lake Biwa and from the Ado River.
Offshore and nearshore distributional patterns of fish larvae were studied on materials obtained 5 to 105 miles off the San-in Coast, the Sea of Japan.The materials consisted of 514 samples containing 3, 528 individuals collected in 1978-1979.The patterns of vertical distribution of major species were classified into three types: (1) subsurface layer: Engraulis japonica, Cololabis saira, Sebastes spp., Stephanolepis cirrhifer; (2) middle layer: Sebastes pachycephalus (?), Etrumeus micropus, Trachurus japonicus, Scomber japonicus, Callionymidae spp., Glyptocephalus stelleri, Hippoglossoides dubius, Paralichthys olivaceus; (3) deeper layer: Glossanodon semifasciatus, Cepola schlegeri (?), Liparidae spp., Triglidae spp., Brotulidae spp., Maurolicus muelleri. The patterns of horizontal distribution were classified as follows: (1) nearshore as-semblage: S.cirrhifer, Triglidae spp., Sebastes spp., S.pachycephalus (?), Liparidae spp.; (2) middle area assemblage: C.schlegeri (?), T.japonicus, G.semifasciatus, Brotulidae spp., G.stelleri, H.dubius, P.olivaceus; (3) nearshore assemblage extending to offshore distri-bution;S.japonicus, Callionymidae spp., E.micropus; (4) offshore assemblage: C.saira, M.muelleri, E.japonica. The distributional pattern of larvae was also considered using a combination of vertical and horizontal distributions.The most outstanding pattern was middle layer-middle area assemblage in 18 principal species. The relationship between the mode of reproduction and distributional pattern of larvae was discussed.Although clear relationship was not found between the two, it was noted that some of the species belonging to the nearshore assemblage produced non-pelagic eggs or were ovoviviparous.Some considerations of the relationship between larval distribution and adult habitat were given.
The present report deals with the fishery biology of Parapristipoma trilineatum, Poma-dasyidae, with particular reference to sex ratio and survival rate, on 1242 individuals taken from coastal areas of Kumano-nada (Kii Peninsula, southern Honshu, Japan) from March 1978 to August 1979. Monthly changes in the sex ratio showed that both sexes are equal in number or males slightly dominate over females all year round except for September.We presume that the predominance of females in September results from increased catches from hand line fish-ing in September when females feed more voraciously than males to compensate for the energy expenditure of spawning.It seems probable that the sex ratio in the population does not change throughout the year.There is little difference in the sex ratio of males to females in 0-3-year age groups, whereas in 4-8-year age groups the ratio evidently decreases.The relationships between the age (x) and the sex ratio (s= _??_/_??_) were expressed by the following equations: for 0-3-year age groups, s=1.21;for 4-8-year age groups, log s= -0.112x+0.423.From the regression of age composition, the survival rates (S) were estimated as follows: for females of 1 3-year age groups and males of 1-4-year age groups, S=0.774;for females of 4-8-year age groups, S=0.490;for males of the same age groups, S=0.387.Changes in the survival rate at 3- or 4-age groups in both sexes are likely to be attributable to the increase of both fishing and natural mortality.