Egg cannibalism by milkfish (Chanos chanos Forsskal) spawners in circular floating net cages

Abstract

Egg cannibalism by milkfish spawners in a circular floating net cage was investigated. The cage was lined with a fine mesh hapa net to retain spawned eggs and to prevent the entry of fish egg predators. Water samples were collected from the surface (0 m), middle (1.5 m), and bottom (3.0 m) of a 10 m diameter by 3 m deep floating net cage at the time of initial detection of spawning (0 min) and at 30, 60, 120 and 240 min thereafter. The mean number of spawned eggs at the surface significantly decreased (P<0.05) 60 min after spawning and very few eggs were recovered 240 min later. There was no significant difference (P>0.05) in the mean number of spawned eggs collected from the middle and bottom of the net cage at various times after spawning. Eggs were found in the digestive tract of all milkfish sampled (n=6) at about 5 h after spawning, indicating that captive milkfish eat their own eggs. It is recommended that spontaneously spawned milkfish eggs should be collected immediately after spawning to avoid loss by egg cannibalism.