Growth, pigmentation and activity of juvenile Japanese eels in relation to temperature and fish size

The growth and activity of juvenile Japanese eels Anguilla Japonica in different pigmentation stages from the glass eel to the elver stage were studied in the laboratory at 15, 20 and 25degrees C. The growth and activity of the eels were significantly influenced by both temperature and fish size. Growth rate generally declined with increasing fish size, and fish were least active and experienced a low growth during the pigmenting stage at all temperatures. They were nocturnal and spent significantly more time moving (swimming, feeding and moving over the substratum) at 20 and 25degrees C than at 15degrees C at night within each pigmentation stage. Accordingly, they grew significantly Faster at 20 and 25degrees C than at 15degrees C throughout the study. The development of pigmentation appeared to be dependant on water temperature but not on fish size. This study suggested that the growth and activity of juvenile Japanese eels were positively correlated, because fish were least active and grew slowest at low temperature (15degrees C) or during the pigmenting stage at all temperatures. (C) 2003 The Fisheries Society of the British Isles.

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c. 17degreesC. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46-52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%). (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank-reared Japanese flounder larvae, Paralichthys olivaceus, had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia. Feeding rates of the larvae prior to 10 days post-batch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19 degrees C. The occurrence of the attack posture, after its onset at first feeding (2 days post-hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19 degrees C. This posture depended on prey density in larvae prior to 10 days post-hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors. (C) 2000 The Fisheries Society of the British Isles.

Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati