Ecological-physiological Studies On Culture Of Reeves Shad And Sunfish

Reeves shad Tenualosa reevesii is a highly valued anadromous fish in China, but is now on the verge of extinction. Despite the studies on its domestication and artificial breeding have been done for decades but the problems still remain unsolved. Therefore, there is an urgent need to find a way to break through this problem. Bluegill, leprosis macrochirus and Fl hybrid female green sunfish L.cyanellus x male bluegill (BxG hybrid) have long been commercially cultured to support recreational fishery stocking needs throughout United State. Recently they have been also receiving much attention as potentially valuable food fish, because of their desirable characteristics for production and the demand for markets. However, the fact that rearing sunfish into at least a third year is necessary to reach food market size has been diminished the suitability of them for commercial production. Hence, there is an urgent need to find a way of reduction of grow-out to 2 years or less.This research was aimed to investigate ecological-physiological characteristics related to cultural problem of these high-valued fishes, and evaluate their potential for commercial aquaculture. The main results are as follows:1. The alkaline phosphatase (AP), lactate dehydrogenase (LDH), alanine aminotransferase (sGPT), aspartate aminotransferase (sGOT) and carbon dioxide (CO2) parameters of serum in Reeves shad were studied before and after handling. The result showed that lack of oxygen which is reflected by increased carbon dioxide levels was a factor resulting in stress and general adaptation syndromome (GAS) of Reeve shad during the course of handling. Therefore, the stress response or general adaptation syndrome was overcome during culture, transportation and handling. It was the first time that shads were domesticated to parent fish from juvenile in captivity.2. In this study we successfully domesticated juvenile shad to 6-year-old for the first time in confined brackish pond with salinity of 0.5-12, and induced gonadal development and maturation with extrinsic pharmacological and ecological manipulations. Induced maturity of 4, 5, 6 year old females reached 85%, 87.5% and 100%, respectively, while controls remained immature. Obstacles to ovulation mechanism and handling-induced stress were overcome in the process of artificial induced spawning through physiological-ecological regulation. Determination of 17p-E2 in blood serum andobservation of development of oocytes following hormonal manipulations were done to verify these results.3. Ovarian development, oogenesis, and spermatozoa formation were in Reeves shad investigated during the course of induced maturation. Ovarian development can be divided into six stages: Oogonium stage previtellogenesis stage, early vitellogenesis stage late vitellogenesis stage, mature stage and spent stage. Oogenesis in Reeves shad is also divided into six phases, i.e. oogonium phase, nuclayer-vacule phase, primary yolk phase, full yolk phase, maturation phase and degenerate phase. The development of primary oocytes from primary yolk phase to full phase is basically synchronous. Fish with this type of development usually spawn one a year. The majority of cultured Reeves shad in pond conditions mature at the age of 4 and 5 by environmental and hormonal manipulations, but the age at the first maturity are 3 years for male and 4 years for female. In autumn, ovaries of spawned shad degenerate to previtellogehesis stage(stage II )from spent stage (stage VI). In winter, the old oocytes of mature female are basically absorbed over, and ovaries are at previtellogenesis stage. In February and March of spring, shad begin to store fat and later, oocytes begin to accumulate yolk material. The ovaries are at previtellogenesis to early virallogenesis stage in May. In summer, ovaries develop rapidly, and reach late vitellogenesis stage by the end of May and mature stage at the middle of July. The development of testes of male is coincident with female during autumn to spring, but faster at summer, and...