Browsing by Author "Takemura, Akihiro"
ArticleA Takemura, Y Takeuchi, T Ikegami, SP Hur, V Soliman, F Ayson, E de Jesus-Ayson & ES Susilo -
Kuroshio Science, 2015 - Graduate School of Kuroshio Science, Kochi UniversityMany teleost fishes inhabiting shallow tropical waters exhibit synchronous spawning around species-selective lunar phases during their spawning season. For example, ovaries of the goldlined spinefoot (Siganus guttatus) develop during a single period each year from June to July in the Ryukyu Islands, Japan, while those of the goldlined spinefoot in the Karimunjawa Archipelago, Indonesia, develop twice a year from March to May, and then again from September to November. Increases in photoperiod and water temperature are possible cues for the initiation of reproductive activity in the populations around the Ryukyu Islands, while the transition between the rainy and dry season may trigger the initiation of reproductive activity in the Karimunjawa Archipelago populations. Moreover, the goldlined spinefoot releases its gametes around the first quarter moon period of the lunar phase, and since the lunar phase is consistent within the Indo-Pacific Ocean, this species can likely perceive cues from the moon and transcribe them as internal signals. In fact, periodical changes in moonlight intensity are expressed as changes in the plasma levels of melatonin, an endogenous transmitter of environmental light/dark cycles. In addition, the mRNA expression levels of clock genes of neural tissues [Cryptochrome (Cry3) and Period (Per2)] change according to changes in the lunar cycle. To date, how the lunar cycle may affect endogenous reproductive processes in fish is not fully understood. However, knowledge of lunar spawning periodicity in commercially important species may help in the management of fisheries resources, determining where and when to prohibit fishing (e.g., time and area closures), as well as promoting efficient aquaculture techniques for inducing synchronous spawning.
mRNA expression patterns for GH, PRL, SL, IGF-I and IGF-II during altered feeding status in rabbitfish, Siganus guttatus. Feeding time is a major synchronizer of many physiological rhythms in many organisms. Alteration in the nutritional status, specifically fasting, also affects the secretion rhythms of growth hormone (GH) and insulin-like growth factor-I (IGF-I). In this study, we investigated whether the expression patterns for the mRNAs of GH, prolactin (PRL) and somatolactin (SL) in the pituitary gland, and insulin-like growth factor I and II (IGF-I and IGF-II) in the liver of juvenile rabbitfish (Siganus guttatus) follow a rhythm according to feeding time and whether these hormone rhythms changes with starvation. Hormone mRNA levels were determined by real time PCR. The daily expression pattern for the mRNAs of GH, PRL and SL was not altered whether food was given in the morning (10:00 h) or in the afternoon (15:00 h). The daily GH mRNA expression pattern, however, was affected when food was not available for 3 days. In contrast, the daily expression pattern for IGF-I mRNA reaches its peak at roughly 5–6 h after feeding. This pattern, however, was not observed with IGF-II mRNA. During 15-day starvation, GH mRNA levels in starved fish were significantly higher than the control fish starting on the 9th day of starvation until day 15. The levels returned to normal after re-feeding. In contrast to GH, PRL mRNA levels in starved fish were significantly lower than the control group starting on the 6th day of starvation until 3 days after re-feeding. SL mRNA levels were not significantly different between the control and starved group at anytime during the experiment. Both IGF-I and IGF-II mRNA levels in starved group were significantly higher than the control fish on the 3rd and 6th day of starvation. mRNA levels of both IGF-I and II in the starved fish decreased starting on the 9th day of starvation. While IGF-I mRNA levels in the starved group continued to decrease as starvation progressed, IGF-II mRNA levels were not significantly different from the control during the rest of the starvation period. The results indicate that aside from GH and IGF-I, PRL and IGF-II are likewise involved in starvation in rabbitfish.
Ovarian development and changes in the serum vitellogenin levels in the river sculpin, Cottus hangiongensis, during an annual reproductive cycle GF Quinitio, A Takemura & A Goto -
Bulletin - Faculty of Fisheries Hokkaido University, 1989 - Faculty of Fisheries, Hokkaido UniversityAnnual changes in the ovarian development and serum vitellogenin concentration were investigated in the river sculpin, Cottus hangiongensis, sampled monthly from a river in southern Hokkaido, Japan. Ovarian development started advancing from summer and continued during the winter months until March with a maximum mean gonadosomatic index (GSI) of 15.99%. Hepatosomatic index (HSI) was also highest in March with a range of 5.13-5.95%. Spawning season usually occured from April to May. Annual changes in serum vitellogenin level correlated very well with the patterns of GSI and HSI, as well as histological changes of the ovary. However, high serum vitellogenin was maintained in March and April.
ArticleP Palma, A Takemura, GX Libunao, J Superio, EG de Jesus-Ayson, F Ayson, J Nocillado, L Dennis, J Chan, TQ Thai, NH Ninh & A Elizur -
Aquaculture, 2019 - ElsevierThe giant grouper is presumed to follow the reproductive pattern of most Epinephelus species, characterized by protogynous hermaphroditism wherein male maturation is attained through sex reversal of a functional female. This hypothesis, however, has not been verified due to lack of biological data. The present study addresses this gap by investigating the reproductive development of giant groupers from juvenile stage through sexual maturity. Gonad histological analysis of hatchery-bred juvenile giant grouper from Queensland, Australia (0.8–5.2 kg, n = 43) have shown earliest occurrence of primary oocytes (i.e. ovarian differentiation) in 47.8 cm and 2.5 kg fish. Monitoring of sexual maturity by gonadal biopsy was performed in a stock of wild-caught giant groupers (2–52 kg) held in sea cages in the Philippines and Vietnam from 2015 to 2017. Onset of female sexual maturity was at 96.9 ± 1.6 cm and 23.5 ± 1.5 kg in the Philippines, and 103.0 ± 4.1 cm and 33.5 ± 2.5 kg in Vietnam. In both locations, development of primary males was observed wherein fish produced milt (or spermiated) without passing through a functional female phase. The ratio of primary males to females in both locations was about 1:2. Size at maturity of primary males is 86.5 ± 4.8 cm and 17.1 ± 2.1 kg in the Philippines, and 97.3 ± 1.3 cm and 34.3 ± 0.9 kg in Vietnam. To aid in the monitoring of female maturation, we developed a non-invasive method based on immunoassay of vitellogenin in skin mucus and this was shown to be effective in detecting female maturation 9 ± 2 months prior to first observation of oocytes through gonadal biopsy. Our findings suggest that giant grouper is a diandric protogynous hermaphrodite. This study provides novel information on the reproductive biology of giant grouper, an economically important and vulnerable species.