Effects of tank wall color and up-welling water flow on growth and survival of Eurasian perch larvae (Perca fluviatilis)

The influence of tank wall color and up-welling water flow on growth and survival of Eurasian perch larvae (Perca fluviatilis) was tested in an intensive culture system. Newly hatched larvae were fed Artemia nauplii, later combined with dry feed, and reared for 5 wk in either black tanks with up-welling water flow or in gray tanks with or without up-welling water flow. The perch larvae grew significantly faster in black tanks than in gray tanks regardless of water flow. Two weeks after hatching, a significantly higher mean weight was shown in larvae reared in black tanks compared to larvae reared in gray tanks with up-welling water flow, and after 4 wk, the mean weight was significantly higher than in both of the other treatments. The difference in growth was further enhanced during the last week of the experiment, and the final mean weights were 51.1 +/- 1.9 mg in black tanks with up-welling water flow, 23.8 +/- 2.1 mg in gray tanks with up-welling water flow, and 23.7 +/- 2.2 mg in gray tanks without up-welling water flow. The cumulative mortality at the end of the experiment averaged 75% in all treatment groups. Taken together, the enhanced growth of Eurasian perch larvae in black tanks could be explained by high prey contrast and increased prey consumption. Up-welling water flow had no impact on growth and survival of the perch larvae in gray tanks, indicating that the availability and consumption of the prey were independent of water movement.