著者

高山 佳樹 山本 翼 戸田 龍樹 Yoshiki Takayama Tsubasa Yamamoto Tatsuki Toda

出版者

創価大学プランクトン工学研究所

雑誌

プランクトン工学研究 (ISSN:24364878)

巻号頁・発行日

no.1, pp.22-31, 2021-06-28

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In aquaculture and ornamental industries, copepods are recognized as preferred live feeds for marine fish larvae over commonly used organisms such as Artemia and rotifers. Marine fish larvae fed with copepods show better survival and growth. Despite obvious advantages of copepods as live feed, their use is still limited owing to low productivity and cost-efficiency when mass cultured. Copepods can be divided into free-spawner and sac-spawner (egg-carrying) according to their spawning style. In cultivation of egg-carrying copepod, a simple nauplii collection/harvesting method with low labor has not been established, because females carry the egg-sac until hatching. Manual collection of nauplii using a siphon hose and mesh-filters is a common method in copepod cultivation, but automation is necessary to reduce labor costs if copepods are to be viably cultured at a commercial scale. Recently, we devised a zooplankton bioreactor for rapid separation of free-spawner copepod eggs from adults in a tank. The automation collects eggs on a mesh filter in a water flow system which can also function as water exchange device. In the present study, we apply this bioreactor to egg-carrying copepod, and report the results from cultivation at laboratory-scale for 45 days. Species of Oithona are good candidates for live feed because their body size and biochemical composition are suitable for many marine fish larvae which have small gapes. Oithona oculata is widely distributed and a typical dominant species in coastal waters, and was chosen as target species of egg-carrying copepod in present study. 150 adult individuals of O. oculata were placed into a culture chamber which were immersed in a reproduction tank containing 3 L seawater. The culture chamber to retain the copepods has a 100-μm nylon mesh placed 5 mm above the bottom, while allowing passage of nauplii. The copepods were fed daily with a sufficient amount of Thalassiosira weissflogii and Isochrysis galbana and incubated at 28°C for 45 days. Produced nauplii in the reproduction tank were collected daily using water flow of 1.5 L min-1. The species abundance in each development, ovigerous rate and collected number of nauplii were measured daily. In the semi-continuous culture, the collected nauplii were cultured in maturation vessels and returned to the production tank after their maturation, and 45 days cultivation (four generations) was achieved. Total abundance was gradually increased from day 4 to day 20 and reached at 500 inds. L-1. Ovigerous rate varied from 0 to 88% during the incubation period. The maximum number of collected nauplii was 380 nauplii L-1 at day 5. The results obtained in present study suggest that the bioreactor can also be applied to egg-carrying copepod by optimization of the mesh size and the water flow velocity.

著者

Kenji Tsuchiya Tomoko Yoshiki Ryota Nakajima Hideo Miyaguchi Victor S. Kuwahara Satoru Taguchi Tomohiko Kikuchi Tatsuki Toda

出版者

The Plankton Society of Japan, The Japanese Association of Benthology

雑誌

Plankton and Benthos Research (ISSN:18808247)

巻号頁・発行日

vol.8, no.2, pp.74-87, 2013-05-25 (Released:2014-08-30)

参考文献数

74

被引用文献数

17 30

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Climate change has the potential for intensification of typhoons, which will cause stronger effects on aquatic ecosystems in the future. The effect of typhoon Mawar (T0511), passing Manazuru Port located in the western part of Sagami Bay, Japan, was investigated from August to September 2005. Immediately after the passage of Mawar, photosynthetically available radiation showed high values, salinity decreased dramatically and nutrient concentrations (NO2+NO3, PO4 and Si(OH)4) increased. Skeletonema spp. and Leptocylindrus spp. were dominant after the passage of Mawar, and their succession was linked to the variability of the N/P ratio. Primary production was highest at 349 mg C m−3 day−1 three days after Mawar, and high assimilation numbers lasted for nine days. The integrated primary production during the nine days after Mawar was 2.1×103 mg C m−3, which accounted for 7.2–9.1% of the annual primary production in the upper waters of Sagami Bay. The study confirms that enhanced primary production induced by episodic typhoon events in temperate coastal regions are significant, and should be considered in annual primary production estimates.