Ichthyological Research最新文献

Chichankanab is a small, shallow, ⁓8,000-year-old, tropical lake where the adaptive radiation of seven sympatric Cyprinodon species have been described. Since the variation in size, morphology, and diet play a key role in facilitating niche partitioning, this study aims to determine if the sympatric species can be independently identified by their variation in size, morphology, and diet and to understand the role of those variables in the ongoing diversification. To fulfill our aim we gathered, from fish collections, an updated sample of the seven sympatric species and the sister species Cyprinodon artifrons from whom we took their size and photographs to develop geometric morphometric analyses, and collected information on their diet. According to our results, size range allows the separation of Cyprinodon beltrani as the largest species, geometric morphometric allows the segregation C. beltrani, Cyprinodon simus, Cyprinodon suavium, and Cyprinodon labiosus, and a morphotype of three species, Cyprinodon esconditus, Cyprinodon verecundus, and Cyprinodon maya, which can be segregated by body measurements and the size of the species. The diet can help to segregate C. beltrani herbivore, C. maya piscivore/omnivore, C. simus zooplanktivore/detritivore, C. suavium and C. verecundus carnivore/molluscivore, and C. esconditus and C. labiosus carnivores. The ongoing hybridization and the changes in the lake are driving the diversification and decrease of these species. According to our results, there is not one character that differentiated all the species, differentiation was only possible through their specific variation in one character or by a specific combination of characters. It is important to monitor and keep updating information on these evolving species since all seven are listed in the IUCN as vulnerable and near threatened, and according to official Mexican categories as in danger of extinction.

Stolephorus brevis sp. nov., a new anchovy from New Guinea, is described, and two similar species [Stolephorus carpentariae (De Vis 1882) (distributed in Gulf of Papua and north coast of Australia) and Stolephorus holodon (Boulenger 1900) (in southeastern coast of Africa)], that have been overlooked taxonomically for more than 30 years, are redescribed. All three species can be distinguished from all other congeners by an indented preopercular margin, numerous gill rakers, and lack of predorsal scutes and distinct markings on the dorsum. The former differ from each other in several characters, including gill-raker counts, pelvic-fin length, and body depth.

Indel (insertion–deletion) events observed in the genome represent irreversible mutational processes, making indel regions crucial characteristics for discussing phylogenetic relationships. The tribe Hippoglossoidini is a recently proposed taxonomic group based on the molecular phylogenetic analyses of both mitochondrial (mt) and nuclear DNA sequences. However, no synapomorphic characteristics have been identified within this tribe, either morphologically or molecularly. In the present study, we sequenced the ND5 region of mtDNA in the righteye flounder species and conducted interspecific comparisons. We found a 12 bp indel immediately upstream of the stop codon in the ND5 region. A comparative analysis of this region with outgroup species from the Paralichthyidae revealed that the indel was a unique insertion shared by the common ancestor of the Hippoglossoidini species, providing irreversible evidence to support the monophyly of this taxonomic group (synapomorphic characters).

Redigobius fotuno sp. nov., described from a limestone sinkhole on Muna Island, Southeastern Sulawesi, Indonesia, is most similar to Redigobius penango (Popta 1922), endemic to the Sulawesi mainland, both species having a robust body and rounded head, reticular body color pattern, and longitudinal suborbital papillae rows. However, the new species is distinguished from the latter in having greater head length (35.3–38.4% of standard length [SL]), upper jaw length (14.7–20.0% of SL) and predorsal length (43.4–46.0% of SL), and a slender pelvic disc with thin frenum (length: 21.7–26.2% of SL; base width: 4.2–6.3% of SL). These unique morphological characters of R. fotuno sp. nov. may be related to the limnetic habitat of the species.

In sympatry, juvenile brown trout (Salmo trutta) usually occupy the shallow and most productive areas (littoral zone) of lakes, while juveniles of Arctic charr (Salvelinus alpinus) are found in deeper, less productive parts. In contrast, when Arctic charr juveniles occur in allopatry, they often occupy shallow littoral areas as well. Habitat segregation has traditionally been interpreted as a trade-off between predation risk and energy gain, while the segregation of these two species has been explained by brown trout being more aggressive and competitively superior to Arctic charr. We hypothesize, however, that the marked habitat segregation between the two species may also be due to differences in predator avoidance. Accordingly, we conducted several laboratory tests, using Arctic charr and brown trout as potential predators. Live fish of the same species were offered as prey, either as small charr only, small trout only, or both small charr and small trout together. Artificial shelters were then introduced to examine the avoidance ability of prey fish against predatory fish. Our results showed that under these circumstances, access to shelters strongly decreased mortality in juvenile brown trout, but had no effect on juvenile Arctic charr mortality. Thus, the habitat segregation shown by sympatric juvenile Arctic charr and brown trout in lakes may be a consequence of interspecific differences in predator avoidance.

Oryzias hubbsi Roberts 1998 is a miniature species of adrianichthyid (medaka). It was described based on a laboratory stock bred from individuals collected in the field in 1983. No individuals of this species have been collected in the field since then. Mitochondrial haplotyping revealed that individuals collected from a fishing pond at Tangerang, west of Jakarta, were Oryzias javanicus (Bleeker 1854), a closely related common species widely distributed throughout the Sunda Islands, as well as O. hubbsi. Phylogenetic network and population genetic structure analyses on the basis of genome-wide single-nucleotide polymorphisms revealed that O. hubbsi and O. javanicus individuals are clearly separated from each other, indicating that they do not hybridize. Morphometric and meristic characters of the newly discovered O. hubbsi individuals were consistent with those of previous studies. We discussed the reasons for the lack of reports of O. hubbsi since the 1980s and the mechanisms of reproductive isolation between O. hubbsi and O. javanicus.

Migrations between spawning, growth and refuge habitats are critical for many fish species. Partially migratory populations of brook charr Salvelinus fontinalis (known as brook trout in the United States), in which a portion of the population migrates, were once widespread in the Great Lakes region of North America, but are now scarce and a rehabilitation priority. Great Lakes fishery managers lack a simple, non-lethal means to determine whether a large brook charr caught in a Great Lakes accessible stream reach represents a stream-resident fish or migrant that previously spent time foraging and growing in Great Lakes waters. We explored a relatively inexpensive and non-lethal stable isotope approach for documenting lake to stream movements of brook charr, using fin clips from brook charr captured in streams in fall prior to spawning. Using fin tissue from juvenile and adult coho salmon captured in Michigan tributaries to Lake Superior, we confirmed distinct stable isotope signatures indicative of prior stream and Lake Superior foraging. We identified brook charr from tributaries accessible to Lake Superior whose stable isotope signatures were similar to those of lake-captured brook charr, lake charr and splake (a brook charr–lake charr hybrid) and distinct from stable isotope signatures of brook charr in streams inaccessible to Lake Superior fishes, suggestive of an adfluvial migratory pattern. Brook charr from two streams had elevated δ¹⁵N values, indicative of previous residency in a downstream lake receiving water from a sewage treatment facility. Our findings demonstrate the utility of stable isotope analysis as a non-lethal technique for confirming adfluvial movements of brook charr from Lake Superior to streams.

Mechanical constraints are one factor that shapes organisms' behavior and morphology. Therefore, elucidating these biomechanics is essential for discovering unknown functions of organisms. The cephalofoil of hammerhead sharks (Sphyrnidae) has long been discussed as representative of the organism's unique morphology and function. While the physiological benefits of cephalofoil are becoming clearer, their kinematic function remains to be elucidated in some areas. Scalloped hammerheads (Sphyrna lewini) have been shown to receive significant hydrodynamic drag during straight swimming due to cephalofoil. In contrast, S. lewini is known to exhibit excellent turning ability, but the hydrodynamic effects of the cephalopod foil during turning have not been clarified. This study performed a numerical fluid dynamics analysis on a simplified 3D model of a cephalofoil to simulate its turning and swinging behavior. The results show that the cephalofoil shape reduces the moment from the fluid by reducing the separation of the flow during turning. The study also suggested that having a cephalofoil creates a trade-off between the efficiency of swimming straight and the ability to turn. This study contributes to our understanding of the function of the cephalofoil in hammerhead sharks and to a deeper understanding of their ecology.

Opsariichthys uncirostris uncirostris (Hasu fish), a vulnerable potamodromous fish, is the only piscivorous cyprinid fish in Japan and endemic as a subspecies to Lake Biwa. The species population is on a continued decline for the past 70 years. This study aimed at developing a portfolio on the species during its reproductive migration to Shiotsuo River, a Lake Biwa tributary, by using a combination of biometric measurements and stable isotope ratios in its tissues. Hasu fish were collected monthly, from May to September 2019, using cast nets. The biometric measurements: wet weight, standard length, gonad weight and gut content were collected and used to calculate the gonado-somatic index (GSI) and Fulton’s condition constant (K) and determine the feeding habits of Hasu fish. Carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) in slow-changing muscle and fast-changing mucus tissues of Hasu fish were also used to determine recent diet change. At the beginning of the reproductive season, fewer females than males were caught; however, the number of females increased as the season progressed. On average, males were larger than females. Migrating individuals were healthy (K > 1) and over 37% larger in length than those in the 1960s. Gut content analysis revealed, for the first time, Hasu fish feeding in the rivers, primarily on Ayu fish, during the reproductive migration. δ¹³C and δ¹⁵N in muscle and mucus indicated a recent change in diet, i.e., from Lake Biwa to Shiotsuo River, with differences in the onset of feeding (and consequently upstream migration) between sexes and individuals. For the effective conservation of Hasu fish in the other tributaries where Ayu fish traps block other fishes’ migration, we recommend having the rivers open from June to September to cover its variable timing in the recruitment of reproductive individuals.