Lethenteron satoi is a species of brook lamprey recently described from a single river in the Ishikari River system, Hokkaido, Japan. To date, the species had been known only from the six specimens used in the original description, and its basic biological information remained extremely limited. Herein, we examined genetic and morphological variation in L. satoi based on 38 individuals collected from four rivers. Mitochondrial DNA analyses revealed that genetic diversity is highest in the lowland areas of the Ishikari River system and that populations are genetically differentiated from one another. Morphological analyses showed that a population from the upper reaches exhibits partially distinct characters and allow us to update the known ranges of metric traits for the species. We also provide new information on the distribution, ecology, and sexual dimorphisms of L. satoi. These findings provide a foundation for future conservation of this recently described species.
It is thought that sex change rarely occurs in high-density populations because small males are able to participate in spawning. We investigated sexual pattern of two wrasses, Halichoeres tenuispinis and Stethojulis interrupta terina, which inhabit Tateyama, Chiba, Japan at high densities, by histological observations on gonads. There were four types of sexual phases: female, IPPM (initial phase-colored primary male), TPPM (terminal phase-colored primary male), and TPSM (terminal phase-colored secondary male). In both species, the number of females and IPPMs was high, but the number of TPPMs and TPSMs was low, indicating that sex change seldom occurred and most IPPM did not change to TPPM. In conclusion, the results show that protogyny and gonochorism coexist and large IPPMs appear in the same population in both species.
Three new species of Neoscopelus (Myctophiformes: Neoscopelidae), Neoscopelus algraham, Neoscopelus ganymede, and Neoscopelus pluto, are described from the Indo-West Pacific, all previously confused with Neoscopelus microchir Matsubara 1943. Together with Neoscopelus serranoi Bañón et al. 2024, they constitute the N. microchir species complex, characterized by a single lateral series of photophores (LO), originating above the pectoral-fin base and extending beyond the anal-fin origin. Within the complex, N. serranoi is distinguished by modal counts of 11 anal-fin rays, 17 pectoral-fin rays, and 3 upper gill rakers (vs. usually 12, 15 or 16, and 4 in the congeners). Neoscopelus microchir is characterized by a large dark blotch on the pectoral-fin base, forming a “D”-shaped mark in large specimens, and usually 3 (1–7) LO on the caudal peduncle; in contrast, congeners have either a “P”-shaped blotch (N. algraham sp. nov.) or a simple dark band (N. serranoi, N. ganymede sp. nov. and N. pluto sp. nov.), and usually 0 or 1 (0–3) LO on the caudal peduncle (except N. ganymede sp. nov.: 2 or 3). Neoscopelus ganymede sp. nov. is further distinguished by a relatively large head, with greater head, snout, and postorbital lengths, and a smaller orbit (snout length 111.1–125.2
Water temperature is a key environmental factor shaping sex determination in many gonochoristic fishes, with direct consequences for population responses to climate warming. This study is the first examination of temperature effects on sex determination in an atherionid fish, a family belonging to a taxonomic group (Atheriniformes) with abundant examples of temperature-dependent sex determination (TSD). It integrates field observations with controlled rearing experiments to analyze the possibility of TSD in the bearded silverside Atherion elymus population of Tokyo Bay, near the northern limit of distribution of this species. Histological analysis of the gonads and daily age estimation using otolith increment analyses indicated that sex determination in wild fish was completed in both males and females at about 14 days after hatching and 10 mm standard length. Reconstruction of the thermal experience of individual fish during this period did not support the assumption of thermal effects on sex determination in wild individuals. Laboratory rearing experiments conducted with five families in environmentally-relevant temperatures also consistently failed to produce sex ratio biases. These results demonstrate that sex determination in the bearded silverside population of Tokyo Bay is largely insensitive to temperature and highlight the importance of integrative field- and experiment-based approaches for assessing temperature effects on sex determination under climate warming. Although the current findings negate the presence of TSD in the bearded silverside, examination of more southern populations is warranted to rule out the possibility of a latitudinal cline in thermal sensitiveness in this species.
The Australian marine atherinid fish, Hypoatherina tropicalis (Whitley 1948), having long been the subject of taxonomic confusion because of its wide intraspecific variation, is redescribed as a valid species based on the holotype and 19 non-type specimens collected from the east coast of Australia. In this process, we describe three new atherinid species, Hypoatherina gracilis sp. nov., Hypoatherina platysoma sp. nov. and Hypoatherina polylepis sp. nov., which were previously confused with H. tropicalis and Hypoatherina temminckii (Bleeker 1854). Hypoatherina gracilis sp. nov. and H. polylepis sp. nov. are distinguishable from all congeners except H. tropicalis in having a short and blunt ascending process of the premaxilla, its height 2.4–2.8 and 2.3–2.8 times the maximum width, respectively, and shorter than half of the premaxillary horizontal length. Hypoatherina gracilis sp. nov. can be distinguished from H. tropicalis by having a narrower interorbital width, 31–33
