| dc.description | Fish stocking is used as a management tool to increase fish production as a source of protein in two multipurpose reservoirs; namely Ubolratana and Huay Luang Reservoirs in the northeast of Thailand. The fishery relies on endemic species and returns of stocked species are apparently very low. This thesis studies the growth and survival in five stock species; namely, bighead carp, grass carp, mrigal, rohu, and silver carp, and a naturally spawning species, tilapia, to determine their relationship to stocking practices and environmental variables, and to measure the economic values obtained from fish stocking programmes. Stocking of three different size-classes (3, 6, and 9 cm) of the five stocked species were conducted from July 1989 to December 1990. Other related experiments included calibration experiments, gillnet experiments, limnological samplings, ground truth sampling for productivity studies by means of LANDSAT remote sensing, fishing-effort surveys, and the cost of seed fish production experiments. Logbook programmes and catch statistics were used to study the human impacts from fishing. The circulus spacing technique was used to estimate instantaneous growth rates in stocked and naturally spawning species. The relative survival rates were calculated to compare the stocking efficiency of each size-at-release. Multivariate regression, multiple regression, and path analyses were used to identify relationships between growth rates and environmental factors in reservoir ecosystems. Profitability and production function and benefit-cost ratio analyses were used to estimate the economic viability of the stocking programmes. The survival rate was best for the 9 cm size-class. The circulus spacing technique is a practical and useful technique for current growth estimation in tropical fish species. The growth rates fluctuated seasonally due to the effects of environmental factors, such as water-level fluctuations, productivity, and temperature. When considered in terms of survival rate, yield, and economic viability, the 9 cm size-class for Indian major carps is recommended for future stocking. Some suggestions are given for future applications in planning fish stocking programmes in Thailand. | en_US |
