Black Rockfish Sebastes Schlegeli Research Articles

Comparison of oxygen consumption patterns between wild and cultured black rockfish Sebastes schlegeli

: To compare metabolic activity rhythms between wild and cultured black rockfish Sebastes schlegeli, we measured long-term oxygen consumption rates (OCR) using an automatic intermittent-flow respirometer under constant temperature and darkness. Oxygen consumption rates peaked among wild black rockfish at 12.4 h intervals, which corresponded to a circatidal rhythm. The wild fish were probably exhibiting responses that corresponded to tidal events in their natural environment. However, when captured wild black rockfish were kept under laboratory conditions (12 h light [L] : 12 h dark [D]) for 30 days, the OCR shifted to a circadian rhythm (24.1–24.9 h). The OCR of cultured black rockfish that had been reared in a tank for 9 months peaked at approximately 24 h intervals, corresponding to a circadian rhythm. The results of this study suggest that the differences in OCR patterns between wild and cultured fish were mainly due to differences in the environmental conditions between tidal and non-tidal habitats.

NaOCl produced by electrolysis of natural seawater as a potential method to control marine red-tide dinoflagellates

As part of the development of a method to control the outbreak and persistence of red tides using sodium hypochlorite (NaOCl), we investigated the effect of NaOCl on the survival of red-tide dinoflagellates, diatoms, heterotrophic protists, planktonic crustaceans, fin-fish, shellfish, and macroalgae. Because NaOCl introduced into natural waters would be subject to dilution, as well as breakdown in sunlight to NaCl, the survival of organisms was determined after 10 min exposure and 1 h exposure to NaOCl, and again after transfer to fresh seawater for 6 or 24 h. The lethal total residual chlorine (TRC) concentration that killed 50% of the test organisms (LC50) for the red-tide dinoflagellates Gymnodinium catenatum, Cochlodinium polykrikoides, Akashiwo sanguinea, Lingulodinium polyedrum, Prorocentrum micans, Alexandrium affine, and Gymnodinium impudicum ranged from 57 to 157 ppb for 10 min exposure and from 30 to 106 ppb for 1 h exposure. Complete mortality of all red-tide species occurred at TRC concentrations of ~ 500 ppb. The LC50 of the diatoms Skeletonema costatum and Thalassiosira rotula, 3083–3383 ppb for 10 min exposure and 3128–3433 ppb for 1 h exposure, were much higher than for red-tide dinoflagellates. But the LC50s of the heterotrophic dinoflagellates Polykrikos kofoidii and Oxyrrhis marina were similar to those of red-tide dinoflagellates. The ciliate Strombidinopsis sp. had LC50s of 306 ppb for 10 min exposure and 119 ppb for 1 h exposure, which are higher than those for dinoflagellates. The LC50s of the calanoid copepods Acarlia spp. and Pseudodiaptomus sp. were 1397–1493 ppb for 10 min exposure and 744–987 ppb for 1 h exposure, and those for larvae of the brine shrimp Artemia franciscana were 4905 ppb for 10 m exposure and 2814 ppb for 1 h exposure. The LC50s of juvenile gray mullet Mugil cephalus and juvenile black rockfish Sebastes schlegeli were 1234–1883 ppb for 10 min exposure and 1234–1440 ppb for 1 h exposure, whereas those of adult Manila clam Ruditapes philippinarum and spat of the abalone Nordotis discus were> 20,000 ppb. The LC50s of the macroalgae Griffithsia japonica (Rhodophyta) and Ulva pertusa (Chlorophyta) were 1519–12,365 ppb for 10 min exposure and 1085–12,558 ppb for 1 h exposure. The present study therefore suggests that, if NaOCl is introduced into waters containing red-tide organisms at TRC concentrations of 300–500 ppb for 10 min exposure and 200–400 ppb for 1 h exposure, red tides can be effectively controlled without serious harmful effects on other marine organisms, except heterotrophic dinoflagellates.

Experimental infection of several fish species with the causative agent of Kuchijirosho (snout ulcer disease) derived from the tiger puffer Takifugu rubripes.

Kuchijirosho (snout ulcer disease) is a fatal epidemic disease which affects the tiger puffer, Takifugu rubripes, a commercial fish species in Japan and Korea. To assess the possibility that non-tiger puffer fish can serve as reservoirs of infection, 5 fish species were challenged by infection with the extracts of Kuchijirosho-affected brains from cultured tiger puffer: grass puffer T. niphobles, fine-patterned puffer T. poecilonotus, panther puffer T. pardalis, red sea bream Pagrus major, and black rockfish Sebastes schlegeli. When slightly irritated, all these species, especially the puffer fish, exhibited typical signs of Kuchijirosho, i.e., erratic swimming, biting together and bellying out (swelling of belly), as generally observed in tiger puffers affected by Kuchijirosho. Although the mortalities of the 2 non-puffer species were lower, injection of the extracts prepared from the brains of both inoculated fish into tiger puffer resulted in death, indicating that the inoculated fish used in this experiment have the potential to be infected with the Kuchijirosho agent. Condensations of nuclei or chromatin in the large nerve cells, which is a major characteristic of Kuchijirosho, were histopathologically observed to some extent in the brains of all kinds of puffer fish species infected. These findings suggest that the virus can spread horizontally among wild and cultured puffers and even among fishes belonging to different orders.

Phylogenetic Intrarelationships of Atypical Aeromonas salmonicida Isolated in Japan as Determined by 16S rDNA Sequencing.

Based on the nucleotide sequences of 16S rDNA, Japanese isolates of atypicalAeromonas salmonicidafrom different fish species can be divided into four groups; isolates from each species of fish (including fish reared in similar culture conditions) always belonged to the same group. Isolates from goldfishCarassius auratushad sequences identical to those from goldfish in the USA and formed the first group. Isolates from Japanese eelAnguilla japonica and marine fishes (greenlingHexagrammos otakii, Japanese flounderParalichthys olivaceus, shotted halibutEopsetta grigorjewi and Schlegel's black rockfish Sebastes schlegeli) formed the second group, and had identical sequences with those ofA. salmonicidasubsp.achromogenes JCM7875T, A. salmonicida subsp. masoucida JCM7873TandA. salmonicida subsp. smithia ATCC49393T. The third and fourth groups composed of isolates from coloured carpCyprinus carpioand common carpC. carpio, respectively. This indicates that the expansion of ulcerative disease in recent years is caused by strains which have phyletic lines different from goldfish isolates.

クロソイ幼魚の温度反応

Studies were conducted to clarify the temperature preference and tolerance, and the effects of temperature on the growth of young Schlegel's black rockfish Sebastes schlegeli. A horizontal temperature gradient tank was used for the temperature preference test. The preferred temperature of the fish acclimated to 15-28°C ranged 17.8-22.8°C, with no clear dependence on the acclimation temperature. The final preferendum was estimated to be about 20.5°C. The upper and lower lethal temperatures of the fish exposed for 72h to eight or nine constant test temperatures ranged 28.1-30.5°C and 2.0-9.5°C, respectively. The critical thermal maximum and minimum ranged respectively 31.2-34.6°C and 1.3-4.9°C. The ultimate upper lethal temperature, which could not be exceeded with elevating acclimation temperature, was 30.8°C. In a rearing experiment, where the fish were fed Euphausia pacifica to satiation for 21 days at seven constant temperatures between 12 and 30°C, the highest daily feeding rate, daily growth rate and food conversion efficiency of the fish were found at 25°C, 22°C and 20°C, respectively.The final preferendum was thus found close to the temperatures for the highest growth rate and food conversion efficiency.

魚類の聴覚特性‐内耳と側線 クロソイの聴覚しきい値とマスキング

魚類の聴覚特性‐内耳と側線 クロソイの聴覚しきい値とマスキング

クロソイの聴覚しきい値と臨界比

The auditory threshold of the black rockfish Sebastes schlegeli was determined by heartbeat conditioning using six pure tone stimuli from 100Hz to 1000Hz, which was coupled with an electric shock. In order to measure the critical ratio, noise was projected to stable spectrum levels at all test frequencies of background noise. Black rockfish could hear a sound in the frequency range from 100Hz to 1000Hz, with greatest sensitivity of 90.7dB at 200Hz. The threshold at 500Hz was higher than others. Until 500Hz the critical ratio increased from 29.7dB to 59.8dB. These results show that the auditory sensitivity of the black rockfish at 500Hz is poor.

クロソイの聴覚しきい値について

The auditory threshold of the black rockfish Sebastes schlegeli was determined by condition-ing method using a sound coupled with bait in a tank. The audio-singnals used were pure tones of 70 to 1400Hz. The mean size of the fishes used in this experiment was 6.53g in body weight and 75.3mm in body length. A positive response was defined by analyzing the swimming performance of the experimental fishes. The fish learned to come to a feeding point in response to the stimulus sounds after 7 to 14 days training. The threshold in sound pressure was 90.6 dB (re 1μPa) at 100Hz which was most stimulative to the fish.