Ichthyological Research最新文献

Evolution of male-biased coloration in the guppy Poecilia reticulata is driven by sexual and natural selection. The colorful male ornaments are attractive to females, but also attract predators. Distinct predation regimes in Trinidadian streams promote the evolution of different guppy color morphs, with male ornamentation and female mate preference also co-evolving among populations. How attractive a male guppy color morph is to a female depends not only on the coloration itself, but also on how strongly the morph evokes stimulation of the female visual system. Both allele type and gene expression levels of cone opsin genes play a role in female mate preferences. Previous studies have demonstrated that predation can alter female guppy mate choice, but the underlying mechanism remains unclear. Here, I hypothesize that guppies adjust their cone opsin expression profiles in response to predation pressure. Although I detected a significant change in LWS-R transcription in response to predation, cone opsin expression profiles in adult female guppies do not appear to be driven by predation pressure. However, the impacts of predation pressure on developmental plasticity in cone opsin expression and brain anatomy remain promising avenues of further investigation to determine how predators affect female mate preference in guppies.

Abstract

Fishes of the genus Rhinogobius (Gobiidae) display paternal care of their nests, constructed beneath stones. Rhinogobius flumineus often coexist with larger Rhinogobius congeners (hence, stronger competitors for the nest site). To understand how R. flumineus reproduce successfully with the presence of a potential nest site competitor, nest-use characteristics of R. flumineus and Rhinogobius nagoyae were investigated in two rivers in southern central Honshu, Japan: one site with both species in sympatry and the other site with R. flumineus in allopatry. Analyses of nest stone, egg clutch, and male body sizes demonstrated that reproductive success, namely the number of eggs deposited, increased with male body size in both species and was positively correlated with nest stone size only in R. nagoyae. The pattern that R. flumineus males are less insistent on using large stones for nesting may partly explain the coexistence mechanism of the two species.

Change in the subtidal reef fish assemblage at Kuchierabu-jima Island, southern Japan, since the 1970s was investigated using an underwater visual census in October 2005. A comparison of this survey with data from 1972 revealed that the frequencies of species that had either increased, remained stable, or declined in abundance were dependent on the geographic range category and the major feeding guild. Temperate herbivorous fishes had noticeably declined in abundance, while subtropical carnivorous species had increased. We discuss causes of the change in the reef fish assemblage from the aspect of water temperature, loss of macroalgal beds, and anthropogenic impacts.

The poacher Podothecus hamlini Jordan and Gilbert in Jordan and Evermann 1898 is redescribed on the basis of 35 specimens collected in northern Japan and southern Okhotsk Seas. This species can be distinguished from Podothecus veternus Jordan and Starks 1895 by the following combination of characters: 2–2.5 rows of dorsolateral plates between the depressed tip of first dorsal fin and the origin of second dorsal fin (almost no space in the latter); plates on caudal peduncle with conspicuous spines (no spine); no black bands on the body behind the head (present); and a black spot present between the 1st and 3rd spines of first dorsal fin (absent). It is suggested that there is no P. veternus in the Japan Sea and that all previous reports of this species are erroneous and refer to P. hamlini.

In recent years, the population of white-spotted charr (Salvelinus leucomaenis) has been declining in the upper reaches of the Daiya River, Nikko City, Tochigi Prefecture. One of the causes is the deterioration of the river environment due to an influx of sediment and construction work. Among the studies investigating the habitat preferences of charr, there are few examples of habitat assessment of stream channels severely altered by artificial structures, such as dams, revetments and concrete riverbeds. For this reason, this study investigated the presence/absence of charr in a reach with sequential low-head dams in the Daiya River that has all those structures. The results indicate that the presence of charr in the altered reach was associated with the abundance of rocks or greater water depth (>20 cm). Based on these results, we conclude that when trying to create a habitat for charr in a stream reach with sequential low-head dams, one should consider adding complexity in terms of rocks and water depth.

Abstract

Two new perchlet species (Perciformes: Serranidae), Chelidoperca pulchella [3 specimens, 58.8–70.4 mm standard length (SL)] and Chelidoperca pollux (3 specimens, 68.1–72.3 mm SL), are described from Okinawa Island, Ryukyu Islands, Japan and Nha Trang Bay, Vietnam, respectively. Both new species are morphologically similar to Chelidoperca flavimacula Psomadakis, Gon and Htut 2021, described from the northern Andaman Sea, but can be readily distinguished from other congeners by the presence of many yellow spots on the anal fin, and three [2 full-sized and 1 (uppermost) half-sized] scales from the dorsal-fin base mid-point to the lateral line. However, the former differ primarily from C. flavimacula in having fewer yellow spots on the anal fin (2 or 3 spots on each membrane between the 3rd to 6th soft rays in the new species vs. 3 or 4 in C. flavimacula), and a single row of mandibular scales extending anteriorly from the angular onto the ventral surface of the dentary (vs. scales restricted to the angular in C. flavimacula). Chelidoperca pulchella is readily distinguished from C. pollux, the former having interorbital scales extending anteriorly beyond the mid-orbit (vs. ending at the mid-orbit), a deeper body (depth at pelvic-fin origin 25.8–26.4% of SL vs. 23.5–24.1% of SL), longer head (length 39.0–39.4% of SL vs. 35.6–36.3% of SL), larger eyes (orbit diameter 13.5–14.1% of SL vs. 11.0–11.7% of SL), and longer pectoral fins (length 27.8–29.8% of SL vs. 24.7–26.4% of SL). Since mitochondrial COI sequences from the type specimens of C. pulchella closely matched that of a specimen from the Philippines, the species may have a widespread distribution on the upper continental slope from the Ryukyu Islands to the Philippines.

The densities of existing fish populations in streams may affect salmonid stocking programs. Non-native brown trout (Salmo trutta) now occur in rivers in Japan that are managed via stocking programs to restore recreational fisheries for native white-spotted charr (Salvelinus leucomaenis), but how they affect charr stocking programs needs to be better understood. We investigate how suppressing populations of brown trout affects the density and biomass of stocked charr population sizes and biomasses. We report no significant change in charr abundance or biomass after stocking into areas in which brown trout are abundant. However, following suppression of brown trout, charr significantly increased in numbers and biomass, and their settlement rates rose in excess of 10 times. We suggest that brown trout outcompete charr for habitat and food resources, and that stocking charr in streams in which brown trout populations exist is unlikely to be effective in the management and restoration of recreational fisheries, but that stocking them into streams in which brown trout have been suppressed is more likely to be effective.

Gobiodon spadix sp. nov. is described on the basis of 37 specimens from Kyushu, and the Osumi and Tokara Islands, southern Japan. The new species is characterized by the following combination of characters: dorsal-fin rays VI-I, 9–11 (modally 9); anal-fin rays I, 8 or 9 (8); pectoral-fin rays 19–21 (20); body depth at pelvic-fin origin 32.4–38.3% (mean 36.0%) of standard length; distance between first dorsal-fin origin to dorsal-most point of pectoral-fin base 50.4–64.8% (55.2%) of head length (HL); pectoral fin relatively long, its length 90.6–112.5% (100.8%) of HL; groove between isthmus and interopercle absent; body uniformly reddish-brown; coloration of all fins darker than that of body; and five narrow vertical bluish stripes on lateral surface of head. The new species is currently known from southern Japan, Papua New Guinea, and northeastern Australia.

Two new species of deepwater cardinalfish, Epigonus gemma [7 specimens, 37.7–76.7 mm in standard length (SL)] and Epigonus hexacanthus (22 specimens, 32.2–57.0 mm SL) are described based on specimens from deep reefs off Curaçao, southern Caribbean Sea. Epigonus gemma is distinguished from other congeners by a combination of the following characters: dorsal-fin rays VII-I, 9–10; pectoral-fin rays 16; total gill rakers 25–27; vertebrae 10 + 15; pyloric caeca 8–9; pored lateral-line scales 43–44 + 5–6; opercular spine absent; maxillary mustache-like processes absent; ribs on last abdominal vertebra absent; tongue toothless; endopterygoid teeth absent; and enlarged conical teeth on symphysis of lower jaw present. Epigonus hexacanthus is distinguished from other congeners by a combination of the following characters: dorsal-fin rays VI-I, 10; pectoral-fin rays 16–17; total gill rakers 25–27; vertebrae 10 + 15; pyloric caeca 6–7; pored lateral-line scales 32–35 + 3–5; opercular spine absent; maxillary mustache-like processes absent; ribs on last abdominal vertebra absent; lingual teeth present; endopterygoid teeth present; and enlarged conical teeth on symphysis of lower jaw absent. Eight specimens (37.6–54.4 mm SL) of E. hexacanthus are female with mature gonads, rendering the species the smallest in size at sexual maturity among its congeners. A key to the species of Epigonus currently known from the Caribbean Sea is provided.

Abstract

Charrs (Salvelinus) reach their southernmost distribution in Japan, and are uniquely adapted to the short, steep streams of this island archipelago. Southern Asian Dolly Varden (Salvelinus curilus) occur only in Hokkaido Island, whereas white-spotted charr (Salvelinus leucomaenis) range to southern Honshu. Both species diverged from an ancestral lineage during the late Pliocene/early Pleistocene, when lowered sea levels created semi-enclosed water bodies in the seas of Japan and Okhotsk. Genetic analyses showed S. curilus represents the most ancient divergence from the Dolly Varden (Salvelinus malma) - Arctic charr (Salvelinus alpinus) group, and revealed five lineages of S. leucomaenis which align differently than traditional subspecies. Japanese charr display diverse and flexible life histories including anadromous fish with partial migration, and fluvial, adfluvial, and resident forms. In Hokkaido, Dolly Varden are distributed upstream and white-spotted charr downstream. They coexist in narrow sympatric zones through adaptive shifts by Dolly Varden in behavior and morphology that facilitate benthic foraging. Both species hybridize with native and nonnative salmonids, and are displaced from microhabitats and decline in abundance when rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) invade. Japan streams contain over 95,000 erosion control dams which create short stream fragments (medians ~200 m). This has increased extirpation of charr populations via lower genetic diversity and stochastic and demographic factors. Tributaries provide complex rearing habitats, afford refuges from floods, and supply recruits that sustain populations in mainstem fragments and create metapopulations in connected riverscapes. Charr play central roles in linked stream-riparian food webs, and cause direct and indirect effects that cascade to streambed algae and riparian predators when linkages are disrupted by anthropogenic effects or altered by native parasites. Many charr populations are threatened by habitat fragmentation and introgression or invasion by nonnative forms, but efforts to conserve charr are growing. These include restoring connectivity among pure populations above barriers that prevent invasions, protecting tributary nurseries, and instituting angling regulations to protect headwater populations. Key steps include inventorying pure populations, identifying conservation units, selecting appropriate management based on connectivity and biotic interactions, and engaging stakeholders and youth to engender an ethic for conserving irreplaceable charr lineages.