Stream bed type, water depth, current velocity and substrate size at the spawning grounds of pond smelt, Hypomesus nipponensis were studied in Kinu River, from April 15 to June 15, 1992, which is one of the inlets of the Yashio Reservoir, Tone River system, central Japan. Pond smelt spawned at flat riffles and pool end from May 23 to June 6. Water depth and current velocity ranged from 10 to 50cm and from 14.0 to 48.0cm/s, respectively and the substrate was sand and gravel at the spawning grounds. Preservation of such environment is important to maintain and enhance the pond smelt population in the Yashio Reservoir.
Features of sagitta, lapillus and asteriscus of laboratory-hatchedOpsaridium microlepis juveniles were investigated. The sagittae were arrow-head shaped, having obvious cores. Increments in the sagittae were observable until rostrum bases but invisible in rostrums. The lapilli were round fun-shaped, having obvious cores. Increments in the lapilli were observable from the core to the edge. Increments counts in the lapilli mostly agreed with actual age in days, indicating the lapillus being applicable for daily increments analysis. The asteriscus was oval-shaped, having ambiguous cores. Increment counts in the asteriscus were fewer than actual age, indicating the asteriscus being unsuitable for aging.
Four intestinal bacteria, which are capable of producing neuraminidase efficiently, were examined for their taxonomic status. Both phenotypic and phylogenetic analyses indicate that strain No. 14 is identical to Photobacterium damselae subspecies damselae and strain Nos. 7, 25 and 52 are a Vibrio shiloi-like bacterium.
To determine the effect of Isochrysis aff. galbana, Clone T-Iso density on the growth of pearl oyster, Pinctada fucata martensii, juveniles (average shell length; 32.9 mm, average whole weight; 3.34 g), T-Iso were fed in various densities to pearl oyster juveniles every day for 34 days. Whole weight, flesh meat weight and glycogen content of the juveniles, which were measured on the initial and final day, increased in juveniles fed 1.5×105 cells/ml/day of T-Iso. However, those of juveniles fed in the densities from 5.0×103 to 7.5×104 cells/ml/day were the same as the initial or below. This result suggests that the required T-Iso for the growth of the pearl oyster juveniles was estimated to be 1.5×108 cells/juvenile /day.
Coho salmon-bowels are disposed as waste derived from food processing industry. Present study was conducted to assess the digestibility of dietary nutrients in extruded pellet (EP) containing 10 and 20% raw coho salmon-bowels on coho salmon, Oncorhynchus kisutch. The test fish weighing 46.6 g on average at the start of the experiment, was reared for 11 days. There was no difference in apparent digestibility of dietary protein and lipid between the diets, 93% and 95%, respectively, while the digestibility of dietary starch of the control and the fish fed the experimental diets containing 10 and 20% raw coho salmon-bowels were 77%, 77% and 82%, respectively. These results suggested that 6% of fish meal and total amount of fish oil can be replaced by raw coho salmonbowels, since EP containing 20% raw coho salmon-bowels can be used for coho salmon.
Efficiency of domestic sewage disposal water on the growth of Heterosigma akashiwo during the early stage of red tide formation was tested under three treatments, namely, (1) domestic sewage disposal water laid on filtered sea water, (2) mixture of domestic sewage disposal water and filtered sea water, and (3) distilled water laid on filtered sea water. Culture was continued for 4 days and repeated three times. H. akashiwo cells collected in sampling area were used as seed for the first inoculation, and H, akashiwo cells which grew in the treatment of sewage disposal water laid on filtered sea water were used for the second and third inoculation. In the treatment (1), cell density increased during the culture period. In the treatment (2), cell density increased during the first 2 to 3 days and kept its density after that. In the treatment(3), cell density increased for 2 days after initiation of culture but decreased rapidly as time elapsed. On the base of those results, there is a possibility that the cell density continues to increase when domestic sewage disposal water is supplied.