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Black porgy are hatched and released in marine ranching areas in Japan, Korea and Taiwan to maintain fisheries resources in coastal areas. If acoustic methods are used for field surveys, target strength (TS) information on the species is needed to convert acoustic data to biomass density. Target strength of black porgy (Acanthopagrus schlegeli) 15.5–32.9 cm fork length (nine individuals) was measured at 38 and 120 kHz (split beam) byex situmeasurements (cage and fishhook methods) of living fish, a tethered method with shock-frozen fish, and an acoustic scattering model, the Kirchhoff ray mode (KRM) model based on fish morphology. Theex situ TS-to-fork length (FL, cm) relationships wereTS38kHz = 20log10 FL − 64.6 (r = 0.77) andTS120kHz = 20log10 FL − 65.2 (r = 0.70). The values for the KRM model wereTS38kHz = 20log10 FL − 64.8 (r = 0.88) andTS120kHz = 20log10 FL − 65.4 (r = 0.80). The agreement between theex situmeasurements and the KRM model for the meanTSwas very good. In contrast, the results for the tethered method (TS38kHz = 20log10 FL − 69.3[ r = 0.42]) differed markedly from the other two methods, perhaps because of the effects of the shock-freezing procedure in air. The results of theex situmeasurements and scattering model provide basic information for studyingTSand conducting acoustic surveys of black porgy, even though the tethered method must be modified. [ABSTRACT FROM AUTHOR]

Age and growth of alfonsinoBeryx splendens(Lowe) were studied using counts of presumed daily incremental growth rings on the transverse section of otoliths of fish collected from the Kanto District, central Japan. Microstructural growth increments were observed from the core to the outermost margin of the broadest of approximately 50 branches formed on the surface of an otolith. Of 98 otoliths examined, 46 were readable. The number of increments and fish lengths ranged from 448 (218 mm fork length[FL]) to 3701 (411 mm FL). The ages of these fish were estimated to be 1 year, 2 months and 10 years, 2 months, respectively, assuming that an increment was formed daily. The von Bertalanffy growth equation combined for males and females was expressed as follows:L t = 542{1 − exp [−0.133(t + 2.00)]}, whereL t is fork length (mm) at yearly aget. The results of the present study were compared with those of other researchers who had studied alfonsino from central Japan. [ABSTRACT FROM AUTHOR]

ABSTRACT: Fish cage farming generates large amounts of organic waste in the form of unconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the impact of fish cage farming on sediment quality, variability of impact and spread of sediment enrichment in the vicinity of a fish farm. Two fish culture sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of the sediment in aquaculture and non-aquaculture areas. The sediment underlying the fish cage farms was found to be extremely reducing, acidic and sulfidic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish farming. A variation in sediment quality within the two sites and also within the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected. [ABSTRACT FROM AUTHOR]