Location: Warmwater Aquaculture Research UnitTitle: Does magnesium hardness in hatching waters affect the fertilization and hatching success of hybrid catfish eggs Author
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2012
Publication Date: 2/21/2013
Citation: Chatakondi, N.G., Jeffers, C.D. 2013. Does magnesium hardness in hatching waters affect the fertilization and hatching success of hybrid catfish eggs. Aquaculture America Conference. P. 182. Interpretive Summary:
Technical Abstract: Embryonic development is deemed to be the most sensitive stage in the life cycle of a teleost. As egg development takes outside the fish’s body, water hardness is one abioitic parameter, suggested to have a major effect on egg development and embryo survival. Ca2+ and Mg2+ contribute to water hardness, and are important for ionic regulation of freshwater fish. These ions influence the permeability of egg membranes, preventing diffusive flow and high ionic loss to surrounding water. Ca2+ ions play an important role in the chain reaction of fertilization in fish eggs in terms of stimulation, reception of stimulation, fertilization and activation of enzymes. Calcium alone or in combination with Magnesium in hatching waters facilitates egg development. However, magnesium hardness alone in hatching waters does not support egg development and fry survival Hybrid catfish are exclusively produced by strip spawning of channel catfish females, fertilizing stripped eggs with blue catfish sperm, and hatching the fertilized eggs. The aquifer used for hybrid catfish hatcheries has less than 10 mg/L of calcium hardness and 1- 25 mg/L of magnesium hardness. Magnesium hardness contributes to 1 to 25% of the total hardness of the hatchery waters, and the effect of magnesium hardness on fertilization and hatching success of hybrid catfish eggs is not known. Hence, this study was conducted to ascertain whether varying levels of magnesium hardness (0, 6, 15 or 30 mg/L) with either fixed (60 mg/L of calcium hardness) or varying levels of calcium (60, 54, 45 or 30 mg/L of calcium hardness) in hatching waters affect fertilization and hatching success of channel x blue hybrid catfish eggs. Basal incubation water contained 0.7 mg/L calcium hardness and 2.7 mg/L magnesium hardness. Desired hardness levels of calcium and magnesium hardness was obtained by adding stock calcium chloride (CaCl2) and magnesium sulphate (MgSO4) solutions. Four independent aquaria rack systems were utilized in this study, each with a particular combination of hardness level was maintained by prepared waters. In the first study, strip spawned eggs from 6 females were fertilized with blue catfish sperm. Hybrid catfish eggs from each females were randomly assigned to two aquaria per (hardness level) rack systems. In the second study, strip spawned eggs from 4 females were fertilized with blue catfish sperm and randomly assigned to four aquaria per (hardness levels) rack system. In both the studies, percent fertilization, neuralation and percent hatch of hybrid catfish eggs incubated in various combinations of hardness waters did not differ (P > 0.05). The results of the study suggest that magnesium hardness (upto 50% of the total hardness) with calcium hardness in hatching waters synergistically facilitates fertilization and hatching success of hybrid catfish eggs.