EFFECTS OF CALCIUM AND MAGNESIUM HARDNESS ON THE FERTILIZATION AND HATCHING SUCCESS OF HYBRID CATFISH EGGS

Hybrid catfish are exclusively produced by strip spawning of channel catfish females, fertilizing stripped eggs with blue catfish sperm, and hatching the fertilized eggs.

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. Previous research has conclusively demonstrated that water hardness is an important environmental factor affecting hatching success of hybrid catfish eggs.

Calcium alone or in combination with Magnesium hardness in hatching waters facilitate fertilization and hatching success of hybrid catfish eggs was evaluated in this study.

A total of 10 different type of waters were tested in this study: Four levels of magnesium hardness (0, 6, 15 or 30 mg/L) with fixed (60 mg/L of calcium hardness); Four levels of magnesium hardness (0, 6, 15 or 30 mg/L) with varying levels of calcium hardness (60, 54, 45 or 30 mg/L of calcium hardness), 1 type of natural water that had calcium and magnesium hardness and 1 type of prepared water that matched the natural water.  Desired level of hardness in prepared water was achieved by adding stock calcium chloride (CaCl₂) and magnesium sulphate (MgSO₄) solutions.

Multiple hatching trails were evaluated in four types of hardness waters and mean percent hatch of hybrid catfish eggs did not differ (Figure 1).  Results of the study suggest calcium is the critical component of hardness and that magnesium has no noticeable effect on egg-hatching success.