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Sato T.,Seikai National Fisheries Research Institute
Aquatic Biology | Year: 2011

In populations subjected to size-selective harvesting of large males, remaining males are small and participate in more matings than in pristine populations. The reproductive rate of such harvested populations can be restricted due to sperm limitation, because the numbers of sperm passed to females decrease with decreasing male size and increasing male mating frequency. Japa - nese populations of the coconut crab Birgus latro are typical examples of populations that are subject to selective harvesting of large males. Reproductive output of the population may have declined via sperm limitation. However, there is no evidence that males exhaust sperm reserves through successive matings, and little is known about the factors causing variations in the number of sperm retained by females in the harvested population. Using field investigations and laboratory experiments, I examined (1) whether males exhaust sperm reserves and (2) what factors cause variations in the number of sperm retained by females. About half of the males had exhausted sperm reserves by the end of the mating season. These males were found to be incapable of further mating or of ejaculating larger numbers of sperm, which was inferred from laboratory experiments. The size of individuals of both sexes participating in mating decreased as the mating season progressed, and males did not adjust ejaculate size in response to female size. Thus, variations in the number of sperm retained by females may have mainly been due to a decline in the male ability to ejaculate large numbers of sperm, due both to increased male mating frequency and decreased male size. © Inter-Research 2011.

Okuzawa K.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Gen K.,Seikai National Fisheries Research Institute
General and Comparative Endocrinology | Year: 2013

Temperature plays a pivotal role in the control of seasonal reproduction in temperate fish species. It is well known that temperatures that exceed a certain threshold impair gonadal development, maturation, and spawning. However, the endocrine mechanisms that underlie these effects are poorly understood. We evaluated the effect of high water temperature on the brain-pituitary-gonadal (B-P-G) axis of a perciform fish, red seabream, Pagrus (Chrysophrys) major during its spawning season (April-May). Fish were reared at either high (24°C: H-group) or optimal/control (17°C: C-group) temperatures for 5 or 10d. After 5d, the transcript abundance of gonadotropin-releasing hormone-1 (GnRH1) in the brain and GnRH receptor (GnRH-R) and FSH-β in the pituitary were significantly lower in H-group than in C-group. Conversely, there was no difference in pituitary LH-β mRNA levels, serum concentrations of estradiol-17β (E2), or the gonadosomatic index (GSIs) between H- and C-groups on Day 5. After 10d, the ovaries of all H-group fish had completely regressed and were filled with only perinucleolar stage primary oocytes and atretic oocytes. The brain GnRH1 expression, pituitary GnRH-R and pituitary LH-β expression, serum E2 concentrations, and the GSI were significantly lower in the H-group on Day 10. Our results suggest that high water temperature is the proximate driver of the termination of the spawning season of female red seabream. The effect appears to be mediated by suppression of gene expression in the B-P-G axis. © 2013 Elsevier Inc.

Sassa C.,Seikai National Fisheries Research Institute | Tsukamoto Y.,Seikai National Fisheries Research Institute
Marine Ecology Progress Series | Year: 2010

Chub mackerel Scomber japonicus and spotted mackerel S. australasicus are important fishery resources in the countries adjacent to the East China Sea (ECS). During February to March in 2004 and 2005, based on species identification using PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of mtDNA, we examined the larval distribution, transport and growth of both species in the southern ECS, where extremely high abundances of Scomber spp. larvae are found. Distribution of S. australasicus was in a more southern area than was S. japonicus, with a higher and narrower range of habitat temperature (20 to 23°C versus 15 to 22°C), although there was some spatial overlap. In 2004, when an intrusion of the warm Kuroshio Branch Current north of Taiwan was evident, S. australasicus were transported northeastward, while they dispersed eastward along the Kuroshio front in 2005 when the intrusion was weak. Although S. japonicus showed a similar pattern of transport and dispersal to S. australasicus, it was more gradual, corresponding with the weaker flow in the northern part of the study area. The daily specific growth rates of S. japonicus and S. australasicus were 6.2 to 8.2% and 7.7 to 9.3% of body length per day, respectively, and growth was significantly higher in 2004 than in 2005 for both species, with both habitat temperature and food availability being higher in 2004. Our study provides fundamental information on the spawning and recruitment of these 2 mackerel species on which to base predictive models, which are essential for protecting these shared stocks that migrate across the boundaries within the ECS. © Inter-Research 2010.

A new epigonid fish, Epigonus mayeri, is described on the basis of two specimens (109.7-113.8 mm in standard length: SL) from off Angola, and Epigonus heracleus Parin and Abramov 1986 is redescribed on the basis of 12 additional specimens with type specimens from off eastern New Zealand.These species belong to a subgroup of Epigonus, known as the "Epigonus robustus group," which have a pungent opercular spine and VII-I, 9 dorsal-fin rays.The new species differs from other species of the group by having a sharp-pointed mustache-like process, presence of a rib on the last abdominal vertebra, vertebrae 10 + 15, tongue toothless, pyloric caeca 5, pectoral fin reaching to vertical line from anus (length 22.2-23.6% SL), orbital diameter 16.4-17.0% SL, head length 37.8-38.0% SL, and lower jaw length 16.7-17.0% SL.© 2011 The Ichthyological Society of Japan.

The dinoflagellate, Heterocapsa circularisquama Horiguchi is known to cause massive marine shellfish deaths in coastal waters of Japan. During the last two decades, proliferation of H. circularisquama across western portions of Japan hampered the production of shellfish cultivation, resulting in economic consequences. In this chapter, the ecophysiology and toxicology of H. circularisquama and subsequent damage to aquaculture are discussed, with special emphasis on the effects of H. circularisquama on the physiology of shellfish. © 2011 Elsevier B.V.

Okamoto M.,Seikai National Fisheries Research Institute
Ichthyological Research | Year: 2012

Two new species of Epigonus are described from the South Pacific. Epigonus chilensis is described on the basis of five specimens (166. 3-208. 3 mm standard length) collected from off Chile. It closely resembles Epigonus lenimen (Whitley 1935), but differs in the presence of a minute tubercle on symphysis of lower jaw, body depth, orbital diameter, and lower-jaw length. Epigonus machaera is described on the basis of eight specimens (157. 2-174. 3 mm standard length) collected from the Chatham Rise, east of New Zealand. It closely resembles Epigonus robustus (Barnard 1927), but differs in the shapes of tongue and two nub-like structures on symphysis of lower jaw and second dorsal-fin spine length. Besides the two new species, 14 species of the genus are characterized by having a pungent opercular spine, more than 40 pored lateral-line scales to end of hypural, and dorsal-fin rays VII-I, 8-10. These species belong to the Epigonus constanciae group, defined in this study. A key to the species in the group is provided. © 2012 The Ichthyological Society of Japan.

Andoh T.,Seikai National Fisheries Research Institute
Comparative Biochemistry and Physiology -Part A : Molecular and Integrative Physiology | Year: 2015

We evaluated whether transcription or translation of the preproinsulin gene or insulin release into plasma is the primary regulator of plasma insulin level in barfin flounder. Three experimental groups were used: one tested 2. h after feeding (. Fed), one tested after fasting for 5. days (. Fasted), and one tested 2. h after feeding following 5. days of fasting (. Refed). No significant differences in insulin transcription, insulin concentrations in the principal islets (PI), or plasma total insulin-like growth factor-I (IGF-I) levels were observed between the three groups. In contrast, plasma insulin level in the Fasted group was significantly lower (P. <. 0.002) than that in the other groups. These results suggest that insulin release is the primary regulator of plasma insulin level and is more sensitive to short-term changes in nutritional conditions than IGF-I level. Furthermore, we estimated the capacity for insulin release. Based on various individual measures, the average insulin stored in the PI was 82.8. μg/kg body weight (BW), and the maximum plasma content of insulin was estimated to be <. 1.7. μg/kg BW. The half-life of plasma insulin in diabetogenic chemically (alloxan) treated flounder injected with insulin was estimated to be 2.79. h, which is much longer than that in mammals, assuming a two-compartment model for the β phase. These results suggest that the capacity for insulin release in fish is ensured by at least two systems, such as the ability to store excess insulin in Brockman bodies, and enhanced efficiency of insulin storage by elongating its half-life. © 2015 Elsevier Inc.

Sassa C.,Seikai National Fisheries Research Institute
Journal of the Marine Biological Association of the United Kingdom | Year: 2010

The feeding habits of myctophid larvae of Symbolophorus californiensis were examined in the southern transition region of the western North Pacific where the main spawning and nursery grounds of S. californiensis are formed. This species is a key component of the pelagic ecosystems of this region, and their larvae attain one of the largest sizes among myctophids. To analyse gut contents larvae, including most life history stages after yolk-sac absorption (3.7 to 22.2mm body length (BL)), were collected in the upper 100m layer in 1997 and 1998. Feeding incidence was higher during the day than at night (53.1-92.3% versus 0-5.6%), and daytime feeding incidence increased gradually with larval growth. Larvae fed mainly on copepods of various developmental stages. Larvae of S. californiensis showed an ontogenetic change in their diet: larvae 7.9mm BL (i.e. preflexion stage) fed mainly on copepod eggs and nauplii, while the larvae ≥8mm BL consumed mainly calanoid copepodites such as Pseudocalanus and Paracalanus spp. In the largest size-class (16-22.2mm BL), the furcilia stage of euphausiids was also an important prey item. There was an increase in the average prey size with growth in larvae ≤11.9mm BL, while the number of prey eaten positively correlated with growth in larvae ≥12mm BL. The trophic niche breadth also increased with larval growth, which would ensure a wide range of available food resources for the larger size-class larvae. Copyright © 2009 Marine Biological Association of the United Kingdom.

Amino acids are important insulinotropins in fish, and their effects vary between amino acids and fish species. Insulin levels are indicative of growth efficiency and stress levels in fish; however, interspecies comparisons of insulin levels are hampered by the difficulty of measuring insulin concentration in each fish. We developed a widely applicable competitive immunoassay using biotinylated yellowtail (Seriola quinqueradiata) insulin for measuring insulin in marine teleosts, including yellowtail and red seabream (Pagrus major), which are the most common species raised by aquaculture in Japan. Amino acid sequence substitution was limited at the ninth residue of the A-chain (A9) between these two species, and analysis of the primary structures of insulins from six phylogenetically far teleosts suggested that the sequences of yellowtail and red seabream insulins are identical to those of many teleosts, except the A9 residue. However, A9 is known to be an epitope that confers cross-reactive differences on insulin. We solved this problem through immunoreactive invalidation of this residue by biotinylation. The binding-inhibition curves of yellowtail and red seabream insulins were identical following the use of this technique. However, yellowtail and red seabream plasma was found to contain components that interfere with immunoassays. This problem was solved by the extraction of plasma using equal volume of acid-ethanol in yellowtail and by cooling at 0. °C during the cross-reaction between the ligand and antibody in red seabream. Serially diluted plasma samples from both species exhibited linearity after these treatments. In a recovery test using plasma with added yellowtail insulin, the average recovery varied from 96.2% to 109.4%. A post-feeding rise in insulin was confirmed by this immunoassay in yellowtail, and peak of the rise was 39.8 ± 7. ng/ml at 1. h postfeeding from 3.9 ± 1.1. ng/ml at 0. h. This indicates that this assay is sufficient for measuring the baseline concentration of plasma insulin after starvation and is a useful indicator of nutritional status in yellowtail, as in other teleosts. This immunoassay demonstrated high performance and resisted interference from plasma components; consequently, it constitutes a useful tool for the interspecies evaluation of insulinotropins and represents a widely applicable insulin immunoassay for many teleosts. © 2015 Elsevier Inc..

Andoh T.,Seikai National Fisheries Research Institute
Fisheries Science | Year: 2014

We evaluated the effect of stress and adrenaline injection on insulin release in barfin flounder Verasper moseri. Flounders were fed to satiation and then exposed to 30 min of stress (chasing using a blunt stick), beginning 15 min after feeding. Plasma insulin concentrations were measured using a time-resolved fluoroimmunoassay for barfin flounder insulin. Peak insulin concentrations in the stressed flounders (3.4 ± 1.0 ng/ml, mean ± SEM) were lower than in the control group (8.3 ± 1.7 ng/ml). Similarly, in flounders injected with l-arginine (Arg; 3.5 mmol/kg body weight), the most potent insulinotropic factor for flounders, insulin levels were lower for up to 5 h in individuals exposed to chasing stress. Furthermore, plasma insulin levels did not increase after injection with Arg followed by exposure to 10 min of stress. This was also true for flounders co-injected with Arg (20 nmol/kg body weight) and adrenalin instead of the chasing stress. We conclude that stress induces a powerful and extended inhibition of insulin release in flounders, even when the stress is acute. We hypothesize that this effect is mediated partly by adrenaline release. Our results provide insight into the deleterious effects of stress on growth. © 2014 The Japanese Society of Fisheries Science.

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