Ichthyological Research最新文献

Opistognathus abei sp. nov. (Perciformes: Opistognathidae) is described on the basis of two specimens (28.5–30.9 mm in standard length) collected from the Oki Islands, Shimane Prefecture, Japan, at a depth of 25–26 m. The new species is characterized by the following combination of characters: posterior end of upper jaw rigid, without flexible lamina; dorsal-fin rays XI, 13; anal-fin rays II, 13; gill rakers 8 + 16 or 17 = 24 or 25; vertebrae 10 + 18 = 28; longitudinal scale rows ca. 40–43; lateral line terminating below 2nd or 3rd soft ray of dorsal fin; cephalic sensory pores comparatively poorly developed, head sparsely covered with small cephalic pores; no scales above lateral line; body scales absent anterior to vertical below 6th or 7th dorsal-fin spine base; vomerine teeth absent; 3rd infraorbital without suborbital shelf; body generally brown, except for white belly, with two longitudinal rows of 6–9 white blotches; head region without blotches, spots, or stripes; dorsal fin generally hyaline to faint brown, with a yellowish-brown stripe through distal edge of spinous part and just below middle of soft-rayed part, and an ocellus between 2nd and 7th spines; anal and caudal fins uniformly hyaline to faint brown; pectoral-fin base with large white oval blotch; pelvic fin uniformly translucent white.

Abstract

Hypoxia is one of the common stress factors encountered in intensive farming. Leiocassis longirostris is a commercially valuable fish with limited information on the response mechanism under acute hypoxia stress. Here, we detected the asphyxiation point and simulated acute hypoxia conditions, dissolved oxygen decreased, hypoxia maintained, and reoxygenation, and investigated molecular changes in the liver of L. longirostris. Results showed that the hypoxia-inducible factor-1 signaling pathway was enriched and hif1α, arnt, hph, epo, epor, and glut1 gene expression significantly increased. Peroxisome proliferator-activated receptor pathway with lipid metabolism-related genes (gk, scd, acsl, pgar, lpl, fabp3) was inhibited, while the glycolysis pathway with its related genes (pk, gapdhs, ldh, pfk, aldo, hk, gpi, pfkfb3) was activated under hypoxia. Furthermore, heat shock protein family gene expression increased significantly in both hypoxia treatments and the reoxygenation group, which suggests that immune response persistent activation was induced by acute hypoxic stress. This study provided valuable information for the metabolism and immune response in L. longirostris liver under acute hypoxia and reoxygenation conditions.

The new snailfish Careproctus rhomboides is described on the basis of four specimens collected from the southern Sea of Okhotsk (570–825 m depth), off Hokkaido, Japan. The new species is most similar to Careproctus bowersianus Gilbert and Burke 1912, with both species having the following characters: teeth trilobed; snout blunt; cephalic pore pattern 2-6-7-2; gill slit small above pectoral fin (or extending down in front of upper ray); pectoral fin shallowly notched; pelvic disk moderately large, ca. 20% in head length; and stomach black. The new species is distinguished from congeners, including C. bowersianus, by the following combination of characters: total vertebrae 59–61; dorsal-fin rays 56 or 57; anal-fin rays 49–52; pectoral-fin rays 32–34; pyloric caeca 13–16; cephalic pore pattern 2-6-7-2, chin pores paired in separate pits; maximum body depth 22.4–30.5% in standard length (SL); inner teeth on both jaws strongly trilobed; pelvic disk oval, slightly longer than width, length 4.3–7.7% SL (18.9–33.9% head length); gill opening small, extending to just above pectoral fin; stomach black and peritoneum pale in preserved specimens.

Most cyprinid fish breed from spring to summer. On the other hand, the timing of initiation and duration of gametogenesis in preparation for reproduction vary widely depending on the species. It is unclear what factors determine the types of timing and duration of gametogenesis. In order to infer the factors, it is necessary to clarify the gametogenesis process of as many species as possible, categorize them, and explore commonalities and differences between species belonging to different types of gametogenesis. In the present study, we determined the maturity of Hemigrammocypris neglecta, a temporary water-spawning fish of the subfamily Oxygastrinae, based on histological observations of the gonads. Female vitellogenesis began in May and continued during the breeding season from May to August. This species was a multiple-spawner that repeatedly ovulates and spawns multiple times during the breeding season. Male spermatogenesis (meiosis) began in April, and a large number of spermatozoa were observed in the testes and sperm duct from May to August, indicating that reproduction is possible during this period. The timing of the initiation of gametogenesis in spring/summer-spawning cyprinid fishes has been roughly divided into three types: autumn type, winter/spring type, and breeding season type. The female H. neglecta was the breeding season type. There are few species that belong to this type, suggesting that the type may have evolved independently with reflect the reproductive ecology of each species. The male is the winter/spring type, a characteristic common to the subfamily Oxygastrinae.

Uncovering the mechanisms driving the genetic divergence of environmentally heterogeneous species is one of the biggest challenges in phylogeography. In the present study, the genetic variation and genetic structure of the Coilia nasus were examined by analyzing thirteen mitochondrial protein-coding genes (PCGs) among 60 individuals collected from 8 populations in affiliated waters of Yangtze River and their adjacent waters. Contrasted to the recently recognized multiple subdivision, our reconstructed phylogenetic tree, analysis of molecular variance (AMOVA), F_ST and haplotype networks refined only two previously recognized clades, with one clade arising from the Dongting and Poyang lakes affiliated to the upper reach of Yangtze River, and the other mainly from the remaining populations. Historical demography analysis revealed that the divergence time between the two clades could be recovered to 60.05 ka, indicating a possible role of late Pleistocene glaciers in their differentiation, possibly via isolation of diverged glaciers’ refugia. Subsequent positive selection test revealed no diverged selective pressures acting on the two clades within all 13 PCGs, suggests that the observed mitochondrial lineage divergence of C. nasus in the Yangtze River and its adjacent waters was primarily driven by neutral evolution. Our results provided new insights into the spatial patterns of genetic variation in population of C. nasus and would provide valuable implications for sustainable management and utilization of this fishery resource in the future.

A new triplefin, Enneapterygius sericus sp. nov. (Perciformes: Tripterygiidae), is described from 51 specimens from the Ryukyu Islands, Taiwan, Indonesia, Australia, and the Solomon Islands. The new species is characterized by the following combination of characters: 9–11 (modally 10) third dorsal-fin rays; ii–v (iv) + 3–6 (4) + iv–viii (vii) = 13–16 (15) pectoral-fin rays; 17–21 (19) anal-fin rays; 15–18 (16) pored lateral-line scales; 32–37 (36) scale rows in longitudinal series; 8–12 (10 or 11) circumpeduncular scales; single transverse scale row between posteriormost pored scale and anteriormost notched scale; mandibular-pore formula usually 3 + 1 + 3; 1st spine of first dorsal fin shorter than that of 2nd dorsal fin, its length 5.5–10.2% (mean 8.2%) of standard length; orbital tentacle short, slender and pointed, its length shorter than nasal tentacle; body generally semi-transparent white with reddish pigmentation; dorsal surface of head with brownish blotches; and head, pectoral-fin base, and abdomen black in nuptial males. Enneapterygius sericus sp. nov. is most similar to Enneapterygius nanus (Schultz 1960), but differs from the latter as follows: 12–14 (modally 13) second dorsal-fin spines [vs. 12 or 13 (12) in E. nanus]; 3 or 3½ scales below 1st notched lateral-line scale [vs. 2 or 2½ (2)]; orbital tentacle slender and pointed (vs. small, leaf-shaped, the edge slightly rounded); dorsal head surface with brownish blotches (vs. unpigmented); lower half of head, opercle, pectoral-fin base, and base of 8 lowermost pectoral-fin rays black on lateral surface; undersurface of head, including pelvic-fin base, and anterior part of abdomen (sometimes extending to anus) black (vs. pectoral-fin base without black pigmentation, black region on ventral body surface reaching or slightly beyond pelvic-fin base). Enneapterygius sericus sp. nov. usually occurs on exposed shallow rocky reefs [in depths less than 5 m off Yaku-shima Island (type locality)]. Spawning has been observed at Yaku-shima Island from the end of February to April.

Anadromous migration of salmonid fish has been extensively studied, primarily focusing on the dichotomous framework of anadromy and residency. However, there remains a limited understanding of intermediate migratory behaviors within the anadromous framework. Our study aimed to classify the lifetime migration patterns of the anadromous white-spotted charr Salvelinus leucomaenis within and among populations using otolith annuli and Sr:Ca ratios. Initially, the migratory histories of anadromous charr were divided into two stages: “virgin sea-run stage” and “veteran sea-run stage”. The former was further categorized into three types: ocean entry at age ≥1+ years old, early descending, and brackish use. The latter was grouped into four types: annual migrants, frequent migrants, retired migrants, and ocean residents. We found that the proportion of migration patterns varied among rivers, with multiple patterns coexisting within the same river. Migration patterns typically involving 1–5 years spent in freshwater rivers followed by annual oceanic migrations were the most abundant, although diverse patterns were also observed. In the virgin sea-run stage, some individuals experienced the ocean at age 0+ years or brackish environments before their first sea entry. In the veteran sea-run stage, we found individuals who had resided in either the ocean or rivers for over a year. Retired migrants, characterized by stopping oceanic migration at a certain age and subsequently spending time in rivers, were exclusive to southern rivers. Conversely, ocean residents who spend one or more years in the ocean were more frequent in northern regions. Consequently, the lifetime migration patterns of anadromous white-spotted charr may exhibit stronger ocean dependency at higher latitudes. The implications of this study highlight the complexity and flexibility of migratory behaviors within and among white-spotted charr populations.

The Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River and is one of the largest freshwater fish. This critically endangered species is a popular food for local people and a commercially essential fishery resource. Ecological knowledge of this catfish is required to conserve it. However, its ecology has not yet been well studied. We monitored the food intake of the Mekong giant catfish in a stable aquarium for over 13 years. We analyzed their feeding rhythms and fasting periods. The feeding rhythm (circannual rhythm) of the Mekong giant catfish over 13 years and its temporal variations were revealed. Four of the six catfish showed feeding cycles that extended more than one year (395.7 days). Five of the six catfish showed prolonged fasting periods over 30 consecutive days. These patterns coincide with the wet/dry seasons in Thailand, corresponding to the abundance of catfish food resources (Cladophora spp.). Furthermore, it is suggested that the Mekong catfish has acquired the physiological ability to tolerate a fasting state for about 1 year, possibly because this species may have survived many critical situations in the Mekong River in the past, such as food insufficiency. At the same time, however, this also indicates that the fish is highly dependent on Cladophora spp. as a food item and may not be able to substitute other food items. From these, reductions in food items or feeding habitats for catfish after damming in many places of the Mekong River basin may decrease the population size of this species.

White-spotted charr (Salvelinus leucomaenis subspp.) and masu salmon (Oncorhynchus masou subspp.) are common stream salmonids in the Japanese Archipelago. In Shikoku Island, although white-spotted charr is not originally distributed, its introduced populations have been established in several streams and caused population decline of red-spotted masu salmon (Oncorhynchus masou ishikawae) in some streams. In this study, we examined effects of non-native white-spotted charr on prey use by native red-spotted masu salmon and described food resource partitioning between the two species at the population and individual levels using their allopatric and sympatric streams. Comparisons of the diet between allopatric (without charr) and sympatric red-spotted masu salmon (with charr) indicated no significant difference at both population and individual levels, suggesting that white-spotted charr had no effect on prey use by red-spotted masu salmon. Comparisons of the diet between red-spotted masu salmon and white-spotted charr in the sympatric stream indicated significant differences at both population and individual levels. The population level analyses showed a clear pattern of partitioning that the diets of red-spotted masu salmon and white-spotted charr were dominated by terrestrial and aquatic prey, respectively. Furthermore, individual-level analyses showed that among-individual variation in prey use was larger in white-spotted charr than in red-spotted masu salmon. The high individual variation in prey use by white-spotted charr may facilitate the coexistence of the two species at the local habitat scale.