Location: Warmwater Aquaculture Research UnitTitle: Effect of calcium and magnesium hardness of incubation waters on the hatching success of female channel catfish Ictalurus punctatus male blue catfish I. furcatus hybrid eggs
Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2018
Publication Date: N/A
Interpretive Summary: Presently, hybrid catfish comprise 60% of the catfish production in US farm-raised catfish industry. Channel catfish x blue catfish hybrid are exclusively produced in hatcheries, however the efficiency of hatchery production has to be improved to meet the demand of hybrid catfish by food fish farmers. The aquifer used for hatcheries has less than 10 mg/L of calcium hardness and 1-25 mg/L of magnesium hardness. Calcium as an essential element in embryonic development of egg. Hatchery waters with 60 mg/L of calcium hardness for optimal hatching success of hybrid catfish eggs was recently determined. Hence, supplemental calcium is supplied to hatchery water by continuous addition of concentrated calcium chloride. The effect of waterborne magnesium in hatchery water may affect hatching success, either specifically or as a component of hardness in general, is not known. Supplementing 0 to 30 mg/L of magnesium hardness after meeting the required hardness criterion of 60 mg/L of calcium hardness evaluated in a hatching trial did not affect the hatching success of hybrid catfish eggs. Magnesium hardness was substituted up to 30mg/L along with calcium hardness to meet the minimal hardness of 60 mg/L in hatching waters. Supplementing magnesium in hatching waters did not affect the hatching success of hybrid catfish eggs in replicated trials. Stripped eggs of high quality were used in both the evaluations to minimize the effects of egg quality on evaluation of hardness waters. Calcium has a specific requirement for the embryonic development of catfish. Waterborne magnesium in hatchery water can be substituted up to 50% of the total hardness of hatching waters. Hatching waters with magnesium hardness can reduce the associated costs of concentrated calcium chloride and the pumping costs. This study will help our understanding on the role of magnesium in egg development to improve the efficiency of hatchery production.
Technical Abstract: Hatching efficiency is generally lower in Channel catfish, Ictalurus punctatus x Blue catfish, I. furcatus hybrid catfish hatcheries compared to hatcheries hatching pond-spawned channel catfish eggs. Egg quality and hatching water hardness are known variables influencing the efficiency of hybrid catfish fry production in hatcheries. Previous research recommended at least 60 mg/L hardness, contributed only by calcium to optimize hatching success of hybrid catfish eggs. However, the effect of waterborne magnesium in hatching waters either alone or in combination with calcium is not known. Two trials were conducted to determine the effects of calcium alone or magnesium hardness, in combination on the hatching success of hybrid catfish eggs. Trial one showed that if the previously identified minimum hardness criterion of 60 mg/L was met by calcium in the hatching waters, added magnesium had no effect on the hatching success of hybrid catfish eggs. Trial two showed that the previously identified minimum hardness of 60 mg/L can be met by either calcium alone or magnesium replacing up to 50% of the total hardness in the hatchery waters for optimal hatching success of hybrid catfish eggs. Calcium has a specific requirement during embryonic development of catfish. The results from this study can be used to design treatment processes for hybrid catfish hatchery water supplies to improve fry-production efficiency.