Assessment of Embryonic and Larval Development of Nile Tilapia under the Traditional and Re-Circulatory Thermostatic System in Relation to Climatic and Water Quality Variations

Abstract

Embryonic and larval development of tilapia (Oreochromis niloticus) is very vulnerable to climate change. This study was conducted for an assessment of the embryonic and larval development of Nile tilapia in traditional hatchery and re-circulatory thermostatic systems. Daily changes in embryonic and larval development were measured through microscopic observation and image analysis in the laboratory. Climatic data and water quality parameters were measured every day using appropriate devices. Water temperature was varied with room temperature at the traditional hatchery system while it was maintained at 28.50 °C in the re-circulatory thermostatic system. A total of 200 unhatched eggs were stocked in every three trays of both systems. The egg diameters of the gastrula, segmentation, and pharyngula stages were measured at higher (2261.47 ± 81.66 µm, 2646.24 ± 17.98 µm, and 2710.90 ± 16.60 µm) in the re-circulatory thermostatic system than in the traditional hatchery system (2261.07 ± 81.52 µm, 2645.47 ± 18.24 µm, and 2710.01 ± 16.45 µm), respectively. For both systems, egg colors, egg size, black pigments, germinal ring, eye shape, tail, and heartbeat were determined through microscopic observation. Higher hatching and survival rates were found under the re-circulatory thermostatic system (95% and 97%) than under the traditional hatchery system (85% and 81%). About 6 h less hatching time was required under the re-circulatory thermostatic system than under the traditional system. At the end of 30 DAH (Days After Hatching), larval length and weight under the re-circulatory thermostatic system were found to be higher (15.736 ± 0.424 mm and 0.0528 ± 0.004 g) than under the traditional hatchery system (15.518 ± 0.415 mm and 0.050 ± 0.004 g), respectively. Larval growth patterns for both systems were found to have an exponential trend. PCA analysis revealed that two components were identified, one primarily associated with morphometric characteristics and the other with climatic and water quality parameters. These components showed that there were several interrelationships between the morphometric changes and the climatic and water quality parameters. The characteristic changes of larval development under the re-circulatory thermostatic system and the traditional hatchery system were found to be remarkably similar except for some deformities denoted under the traditional hatchery system. The changes of yolk sac, body pigmentation, dorsal and caudal fin shape, eye size, and head length and width were determined from 1 DAH to 30 DAH. After absorbing the yolk sac, ready-made feed was provided. The water temperature was varied from 30.50 °C to 35.50 °C in the traditional hatchery system. The highest air temperature and humidity were 33.87 °C and 69.94% while the lowest were 29.63 °C and 45.62%, respectively, in the traditional hatchery system. There has been no such comprehensive comparative study on hatchery production in Bangladesh, and therefore, further research might be carried out on broader aspects. This research would be highly beneficial for improving seed production at the tilapia fish hatchery level in the country.