Tetsuo Iwami

The summer diet of demersal fish at the South Shetland Islands

The stomach contents of demersal fish in late January 1982 were analysed. Samples were taken at 100, 300 and 500 m depth south of Elephant Island, Bransfield Strait and north of Livingston Island, and at 800 m to the east of Smith Island. Fifty four taxa of fish belonging to 11 families were collected. The diets of 2101 fish representing 38 taxa were examined. These were classified into three categories, fish feeders, krill feeders and benthos feeders. Fish prey species fed on krill and/or benthos. Krill was a major dietary component for 32 (84.2%) out of 38 taxa. Gobionotothen gibberifions was distributed at all 10 stations (lo& 800 m in depth) and its diet comprised krill and benthos. The present findings verify the importance of krill in the Antarctic marine ecosystem and indicate that krill is consumed by benthic fish at greater depths than previously reported.

Ecological studies on the community of drifting seaweeds in the south‐eastern coastal waters of Izu Peninsula, central Japan. I: Seasonal changes of plants in species composition, appearance, number of species and size

Seasonal patterns of drifting seaweeds in the southeastern coastal waters of Izu Peninsula of central Japan were examined by sampling 966 patches from spring to autumn 1991–1993. In total, 57 plant species appeared, including 10 epiphytic algal species. Monthly totals of the number of species, excluding epiphytic aigae, were highest in May (33) and August (27), though 19–21 species of sargassaceous algae were found from May to August, The number of species, excluding epiphytic algae, in one patch of drifting seaweeds was 1 to 11 (x̄= 2.93 ± 2.06) with high richness in May a result of almost entirely sargassaceous species. The wet weight of each patch and maximum stipe length of plants varied from 5 to 6970 g and from 20 to 840 cm (x̄= 536.1 ± 782,3 g and 110.6 ± 76.8 cm), respectively, with highs in April and May. Out of 18 species common to all years, 10 species dominated the top or second rank in monthly pooled frequency of appearance. Seasonal changes of these 10 major species were examined, Sargassum horneri (Turner) C. Agardh and Hizikia fusiformis (Harvey) Okamura were abundant in April, but were replaced partly by Sargassum muticum (Yendo) Fensholt in May and largely by Sargassum yamamotoi Yoshida in June. In July, Sargassum nipponicum Yendo and Sargassum piluliferum (Turner) C. Agardh dominated. Subsequently, the major species shifted to Sargassum ringgoldianum Harvey and S. yamamotoi in August, Sargassum micracanthum (Kützing) Endlicher, Sargassum macrocarpum C. Agardh and Zostera marina Linnaeus in September, and S. ringgoldianum and S. micracanthum in October. However, the occurrence of S. yamamotoi, S. nipponicum and S. piluliferum in June or July were particularly heterogeneous compared with other areas of Japan. Dendrogram analysis was done based on frequency of appearance. Pooled monthly samples were divided into three groups characterized from the dominant species, degree of domination, weight, length and number of species of drifting seaweeds as well as the degree of diversity or evenness in appearance. This characterization indicated that the diversity and abundance of drifting seaweeds were higher from April to June than in later months.

Taxonomic studies of the Antarctic icefish genus Cryodraco Dollo, 1900 (Notothenioidei: Channichthyidae)

Abstract. Based on a meristic and morphometric study of 101 specimens, we recognise 2 valid species in the Antarctic channichthyid genus Cryodraco: Cryodraco antarcticus Dollo, 1900 and C. atkinsoni Regan, 1914. Although the species overlap in most meristic and morphometric characters, we have distinguished several reliable characters for diagnosis and identification. Multidimensional scaling, a nonparametric multivariate technique, clearly separates the two species on the basis of pelvic fin length, head length, number of second dorsal fin rays and origin of the lower lateral line relative to the anal fin rays. We provide a revised identification key to the species of Cryodraco. From a zoogeographical point of view, C. antarcticus has a circum-Antarctic distribution whereas C. atkinsoni is largely confined to the East Antarctic Zoogeographic Province.

A study of the systematics of cyprinid fishes by two-dimensional gel electrophoresis

This study was carried out to shed light on confused subfamilial groupings in the Cyprinidae from the biochemical viewpoint at the molecular level, specifically by using two-dimensional gel electrophoresis of liver proteins. Six pairs of cypriniform fishes, which are different from one another at familial, subfamilial, generic, specific, subspecific, and individual levels, were compared. The genetic distances between pairs of fishes increased as taxonomic ranks of the pairs became higher, confirming the reliable usefulness of this technique. Four species representing the different subfamilies, Cyprininae, Gobioninae, Acheilognathinae, and Leuciscinae, were compared to give new insight into relationships at the subfamilial level. Cyprinus carpio (Cyprininae) and Pseudogobio esocinus esocinus (Gobioninae) gave the smallest genetic distance and the largest values were obtained between either one of the above species and Acheilognathus melanogaster (Acheilognathinae), suggesting that the former two subfamilies compose the most closely related group that is in turn distantly related to Acheilognathinae. Tribolodon hakonensis (Leuciscinae) had almost equal genetic distances to the three other species.

Retinal topography of ganglion cells and putative UV-sensitive cones in two Antarctic fishes: Pagothenia borchgrevinki and Trematomus bernacchii (Nototheniidae).

Abstract Accessory corner cones (ACC) have recently been suggested to be UV-sensitive photoreceptor cells. With a view toward explaining prey detection, we examined the topography of retinal ganglion cells and ACCs in two Antarctic nototheniids occupying different ecological niches: the cryopelagic Pagothenia borchgrevinki and the benthic Trematomus bernacchii. Isodensity maps of retinal ganglion cells showed that the main visual axis, coincident with the feeding vector, was in a forward direction in both species. Visual acuity was determined as 3.64 and 4.77 cycles/degree for the respective species. In P. borchgrevinki the highest density of ACCs was associated with the eyes main visual axis. This suggested that this species uses UV-vision during forward-swims and probably in encounters with prey. On the other hand, T. bernacchii possessed two horizontal band-shaped high-density areas of ACCs, which stretched from temporal to nasal and ventral to peripheral retinal regions. Therefore, this species appears to use UV-vision to watch prey across the entire circumference of the lateral area and in the water column above its head.

Phylogenetic analysis of Antarctic notothenioid fishes based on two-dimensional gel electrophoresis

Abstract. There has been some controversy over the phylogeny of Antarctic notothenioid fishes among researchers. In this study, total protein constituents of cardiac muscles from six well-known notothenioid species were compared by two-dimensional gel electrophoresis to obtain comprehensive phylogenetic information to shed light on the controversial issues. Our phylogenetic analyses showed that Gymnodraco acuticeps (Bathydraconidae) and Champsocephalus gunnari (Channichthyidae) composed a sistergroup, and that the family Nototheniidae was paraphyletic, because nototheniid Gobionotothen gibberifrons was more closely related to the bathydraconid-channichthyid clade than to the clade composed of three other nototheniid species. Our data also showed that Trematomus bernacchii was more closely related to Pagothenia borchgrevinki than to congeneric T. eulepidotus, suggesting that the taxonomic status of P. borchgrevinki or T. bernacchii should be re-evaluated. Since our results were supported by nucleotide sequence data on rRNA genes, phylogenetic relationships of Antarctic notothenioids have become more entrenched by molecular approaches at both protein and DNA levels.

Comparative morphology of the adductor mandibulae musculature of notothenioid fishes (Pisces, Perciformes)

The jaw musculature of notothenioid fishes is described and compared based on a total of 38 species referred to eight families of the suborder Notothenioidei. In the Notothenioidei, the adductor mandibulae, the largest and most conspicuous of the cranial muscles, is generally composed of sections A1, A2, A3 and Aw as in the generalized percoids. The morphology of the adductor mandibulae is similar in most notothenioid families except the Nototheniidae and Bathydraconidae. Notothenia, Paranotothenia and Dissostichus are clearly distinguished from the other nototheniid genera in having A3. Gymnodraco of the Bathydraconidae has a fused A1-A2 complex and the anterior element is segmented by a tendinous intersection from the A1-A2 complex. These features are unique to Gymnodraco and not seen in other bathydraconids. The Harpagiferidae and Artedidraconidae share the same apomorphy, the presence of A1β, with the Nototheniidae and have no synapomorphies with the Bathydraconidae and Channichthyidae. The character distribution, however, shows some inconsistencies with the previous classifications. Based on the limited evidence obtained in this study, the Notothenioidei can be divided into six groups and it seems reasonable to suggest a review of the current classification of the Nototheniidae.

Ecological studies on the community of drifting seaweeds in the south-eastern coastal waters of Izu Peninsula, central Japan. II: Seasonal changes in plants showing maximum stipe length in drifting seaweed communities

The authors examined seasonal patterns in 20 sargas‐saceous species (maximum stipe length of ≥45 cm) from 902 patches of drifting seaweeds in the southeastern coastal waters of the Izu Peninsula, central Japan, between spring and autumn, 1991–1993. The first analysis, dealing with plants occurring for three consecutive years, examined the top three ranked species determined from monthly pooled means of frequency of appearance in these 3 years. The second analysis examined not only the top‐ranked species in monthly means in each year, but also the continuity of appearance of species among years. The third analysis was made from dendrogram analysis based on monthly samples from each year. The first and second analyses revealed three seasonally discernible changes. From April to June, dominance shifted from Sargassum horneri (Turner) C. Agardh to Sargassum yamamotoi Yoshida with a stable transition; in July, S. yamamotoi, Sargassum macrocarpum C. Agardh, Sargassum crispi‐folium Yamada and Sargassum piluliferum (Turner) C. Agardh appeared consistently in an unstable domination with low frequency of appearance by Sargassum nipponicum Yendo, Sargassum fulvellum (Turner) C. Agardh, S. macrocarpum or S. crispifolium; in August to October, there was a stable shift from S. macrocarpum to Sargassum micracanthum (Kützing) Endlicher and Sargassum ringgoldianum Harvey. In the third analysis, monthly samples from each year were divided into four groups, characterized using the top five ranks. This characterization indicated that the top‐ranked species shifted from S. horneri to S. yamamotoi, to S. macrocarpum and to S. micracanthum with the change of seasons. Because of an overlap in the characteristic species in these three analyses, seven species (S. horneri, S. micracanthum, S. yamamotoi, S. macrocarpum, S. ringgoldianum, S. nipponicum and S. crispifolium) were regarded as dominant species. Results are compared to our previous study and it is suggested that the similarity in the pattern of plant community during seasonal changes over the period from April to June and in July resulted from both stable and unstable changes, respectively, but discrepancies in the pattern of plant community during seasonal change from August to October were the result of differences in the frequency of appearance of S. ringgoldianum and S. macrocarpum in August 1991. These results indicated that the seasonal changes of dominant species in the plant community from April to October in this study area were periodic except in July.