High reproductive potential of the commercially exploited shark Squalus suckleyi in the major fishing grounds of the western North Pacific.

The present study examined body length (precaudal length, PCL) and age at sexual maturity, as well as fecundity and maternal investment in the Pacific spiny dogfish Squalus suckleyi, a long-term commercially exploited shark in the western North Pacific, using samples caught in several fisheries and across seasons. The PCL and age at 50% sexual maturity of males were 60.6 cm and 9.4 years, respectively, and those of females were 73.1 cm and 17.8 years, respectively. The PCL and age at 50% maternity were 77.4 cm and 19.7 years, respectively. General or generalized linear models revealed that capture by different fishing method did not significantly correlate with sexual maturity and maternity rates or litter size. Other general linear models revealed an increase in offspring size with maternal size, but litter size was not affected by embryonic development. These findings indicate that the reproductive potential of Pacific spiny dogfish is relatively high throughout the whole North Pacific region because of a smaller size and earlier age at sexual maturation in both sexes. In addition, pregnant females displayed no resting phase and produced 0.45 more embryos per centimetre of PCL in their lifetime after the onset of maturity, which is higher than in the eastern North Pacific. We suggest that these qualities are not a consequence of stock decline associated with the long-term exploitation of the species, but that its high reproductive potential has likely contributed to the long-term stability of the landings in Japan. SIGNIFICANCE STATEMENT: While reproductive potential has been determined for many fish species, such information is scarce for Pacific spiny dogfish. We evaluated the reproductive characteristics of this species in the major fishing grounds of the western North Pacific. The productivity and rebound potential of sharks is extremely low compared with those of bony fishes. However, our results indicate that even if the reproductive potential has a small effect on the population dynamics, it should not be ignored for sustainable stock utilisation.

Early life history affects fish size mainly by indirectly regulating the growth during each stage: a case study in a demersal fish.

The complex life histories of demersal fishes are artificially separated into multiple stages along with changes in morphology and habitat. It is worth exploring whether the phenotypes expressed earlier and later during the life cycle are related or decoupled. The life stages of first year Pacific cod (Gadus macrocephalus) were tracked over different hatch years and regions to test whether the early life history had a long-lasting effect on subsequent growth. We further explored the contribution of growth in the early and subsequent life history stages to body size at the end of each stage. In addition to the accessory growth centre and the first annual ring, the other two checks on the otolith possibly related to settlement and entering deeper waters were identified in 75 Pacific cod individuals. The direct and indirect relationships among the life history stages was interpreted based on path analysis. The results showed that growth prior to the formation of the accessory growth centre had a significant effect on the absolute growth of the fish before and after settlement and migration to deep water. However, there was no or moderate evidence that early growth affected the body size at each stage, which was mainly regulated by growth during the stage. This study supports the lasting effect of early growth and clarifies that it affects size mainly by indirectly regulating staged growth. Quantifying the phenotype relationships and identifying the internal mechanisms form the basis for assessing population dynamics and understanding the processes behind the changes. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-022-00145-y.

Taxonomic revision of the genus Lycenchelys (Osteichthyes: Zoarcidae) in Japanese waters.

Eelpout species of the genus Lycenchelys Gill, 1884 recorded from Japanese waters are taxonomically revised. This study recognizes the following 11 species from Japanese waters as valid: Lycenchelys albomaculata Toyoshima, 1983, Lycenchelys aurantiaca Shinohara Matsuura, 1998, Lycenchelys hippopotamus Schmidt, 1950, Lycenchelys maculata Toyoshima, 1985, Lycenchelys makushok Fedorov Andriashev, 1993, Lycenchelys melanostomias Toyoshima, 1983, Lycenchelys rassi Andriashev, 1955, Lycenchelys remissaria Fedorov, 1995, Lycenchelys ryukyuensis Shinohara Anderson, 2007, Lycenchelys squamosa Toyoshima, 1983 and Lycenchelys tohokuensis Anderson Imamura, 2002. We redescribe species in detail based on type specimens as well as additional specimens in many cases. The synonymy of Lycenchelys brevimaxillaris Toyoshima, 1985 with L. melanostomias is supported in this study. Sexual dimorphism and changes with growth are revealed in L. albomaculata, L. aurantiaca, L. hippopotamus, L. makushok, L. melanostomias and L. rassi, all based on 10 or more specimens, for relative head length, head width, and upper and lower jaw lengths. In addition, we also found that the sizes at which sexual dimorphism can be recognized, and the tendencies for change with growth, differ among species. Furthermore, the dimorphism in head length is influenced by the snout length, eye diameter and/or postorbital length in L. albomaculata and L. aurantiaca.

A new species of snailfish of the genus Paraliparis (Liparidae) from the western North Pacific, with a redescription of the poorly known species Paraliparis mandibularis.

A new snailfish, Paraliparis flammeus, is described on the basis of 18 specimens collected off the Pacific coast of Tohoku District, northern Japan at depths of 422-890 m. The new species is distinguished from 28 species of Paraliparis described from the North Pacific by the following combination of characters: mouth oblique; uppermost pectoral-fin base below horizontal through posterior margin of maxillary; 60-63 vertebrae, 54-58 dorsal-fin rays, 50 or 51 anal-fin rays, six principal caudal-fin rays, and 17-20 pectoral-fin rays. A maximum likelihood tree based on 106 COI gene sequences (492 bp) of Paraliparis recovered a monophyletic group comprising P. flammeus, Paraliparis cephalus, and Paraliparis dipterus. Paraliparis cephalus is similar to P. flammeus in having an oblique mouth, but it has four caudal-fin rays (vs six rays) and the uppermost pectoral-fin base above a horizontal through the maxillary posterior margin. Paraliparis dipterus differs from P. flammeus in having a horizontal mouth, 12-14 pectoral-fin rays, and lacking pyloric caeca (present in P. flammeus). Paraliparis flammeus is most similar to the eastern North Pacific Paraliparis mento in having an oblique mouth and the uppermost pectoral-fin base below a horizontal through the posterior margin of the maxillary. However, P. flammeus differs from P. mento in having six caudal-fin rays (vs five rays) and greater preanal length (29.9-35.3% SL vs 26.7-28.5% SL). A poorly known species, Paraliparis mandibularis, previously known from only two specimens collected from Tosa Bay, southern Japan, is redescribed based on the holotype and seven newly collected specimens. It is also similar to the new species but has 27-30 pectoral-fin rays and a shorter pectoral-fin lower lobe (13.8-15.9% SL in P. mandibularis vs 16.7-23.4% SL in P. flammeus).

A novel growth function incorporating the effects of reproductive energy allocation.

Ontogenetic growth functions provide basic information in biological and ecological studies. Various growth functions classified into the Pütter model have been used historically, regardless of controversies over their appropriateness. Here, we present a novel growth function for fish and aquatic organisms (generalised q-VBGF) by considering an allocation schedule of allometrically produced surplus energy between somatic growth and reproduction. The generalised q-VBGF can track growth trajectories in different life history strategies from determinate to indeterminate growth by adjusting the value of the 'growth indeterminacy exponent' q. The timing of maturation and attainable body size can be adjusted by the 'maturation timing parameter' τ while maintaining a common growth trajectory before maturation. The generalised q-VBGF is a comprehensive growth function in which exponentials in the traditional monomolecular, von Bertalanffy, Gompertz, logistic, and Richards functions are replaced with q-exponentials defined in the non-extensive Tsallis statistics, and it fits to actual data more adequately than these conventional functions. The relationship between the estimated parameter values τ and rq forms a unique hyperbola, which provides a new insight into the continuum of life history strategies of organisms.