Time filter

Source Type

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. Source

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. Source

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. Source

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. Source

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. Source

Discover hidden collaborations