Effect of tank colour on foraging capacity, growth and survival of milkfish (Chanos chanos) larvae

Abstract

Larviculture of milkfish (Chanos chanos) associated with issues like larval deformity, mass mortalities which contribute in variable seed production. Effect of abiotic factors as rearing tank colour and illumination on larvae foraging behaviour, prey localization and ingestion were investigated to improvise milkfish larval rearing system. Reinforced Cement Concrete (RCC) tanks (capacity, 8 t; water salinity, 32 ppt) with three different background colors, white, blue and yellow were divided in five (05) treatment groups with triplicates, i.e. indoor white (T1/C), blue (T2), yellow (T3) color tanks with artificial illumination and semi outdoor blue (T4), yellow (T5) color tanks with solar illumination. Newly hatched milkfish larvae (tl., 3.4 mm) were stocked in the experimental tanks @ 2.5 no l−1 and apart from background colour and source of illumination uniform water quality and feeding regime were maintained in all treatments. Phytoplankton, Chlorella salina @ 103–104 cells ml−1 were maintained from 2 dph to 20 dph; Chlorella grown rotifers, Brachionus plicatilis (enriched with Nannochloropsis oculata paste) were provided @ 20–30 no ml−1 from 3 dph to 14 dph depending on the larval density. Artemia nauplii @ 0.5–1.0 no ml−1 was introduced from 15 dph. At the end of the experiment- 20 dph, highest (p < 0.05) larval survival (45 ± 5.63%) was achieved in tanks providing yellow background colour (T5) compared to control and other treatments. Larval growth (tl., 17.1 ± 1.37 mm) was also found to be highest (p < 0.05) in T5. Increased survival and growth of milkfish in T5 was synchronized with significantly higher (p < 0.05) specific growth rate (SGR), larval gut content relative to other treatments. Milkfish larvae being a day feeder did maximum foraging during 0700 h to 1600 h evident from decreeing prey abundance during that period and as a result positive correlation found between larval standard length and gut content. Larval visibility enhancement in solar illuminated yellow tank act synergistically to perform necessary foraging to acquire nutritional energy for metamorphosis to fry. Above phenomenon may not have occurred in other treatments except T5 and partially in T3. Solar illuminated yellow colour tanks significantly contribute towards mass scale seed production of milkfish.