A Fundamental Study on the Behaviour of Milkfish Fry for Improving the Efficiency of Traditional Fry Collecting Gear in the Philippines

The reaction of milkfish fry to moving and stationary nets of different meshes and colors in an experimental tank was determined. The underwater visibility of the nets was measured and the water filtration in a fry-sweeper was observed. Milkfish fry were both driven well by the moving nets and retained well by the stationary nets, with the fine-meshed black net most effective in both cases. The white and blue nets were found to be quite invisible to the fry in the blue-painted tank, particularly under contour lighting conditions; the black net was found to be very visible to the fry under both surface and contour light. The underwater visibility of the nets was found to vary with the sea conditions and the light direction. Water filteration in the fry-sweeper was found to be almost perfect. From the results, it was concluded that milkfish fry are caught by the moving fry collecting gear through driving and not by filtering. Since fry collection grounds are usually turbid, it was recommended that dark-colored materials be used for effective driving. It is also deemed much better to use larger mesh nets in the wings of the fry gear to minimize net resistance in the water and facilitate operation