Method for efficiently obtaining fertilized eggs from the black scraper Thamnaconus modestus by natural spawning in captivity

To develop an efficient and stable method for enhancing spawning of black scrapers in captivity, we examined the following three factors: (1) different kinds of spawning substrate, (2) the area of the spawning substrate, (3) the grain size of the spawning substrate. The results demonstrated that sand is the optimum spawning substrate when compared to a hard polyvinyl chloride sheet, a piece of shading net, or artificial spawning grass. No difference was observed in the spawning frequency between a small sand bed of area 400?cm² and sand spread over the bottom of the tank to an area of 7085?cm², since the egg masses were spawned on the sand in a small area approximately 15?cm in diameter. In addition to the spawned eggs, the small movable sand bed is useful for subsequent harvest. No differences were observed in either the spawning frequency or the hatching rate when using sand beds with different grain sizes. In large-scale egg collection trials, an average of 33 egg masses from which an average of 403,000 larval fish were obtained. We can therefore conclude that the procedure developed in the present study is applicable to the commercial-scale seed production of black scraper.