The effect of tank colour on background preference, survival and development of larval swimming crab Portunus trituberculatus

The cultured swimming crab Portunus trituberculatus could be supplied out of season and achieve high-added value, leading to rapid development of P. trituberculatus culture industry. However, little knowledge is known in indoor seeding of swimming crab, creating a gap between seed supplies and farmer's demand. Optimizing background colour is essential for maximizing the larval performance of P. trituberculatus. The purpose of this study is to evaluate the colour preference of swimming crab larvae, and the effect of tank colour on survival, development and oxygen consumption rate from zoea I to megalopa. Tank colours evaluated were red, yellow, black, blue, green and white. A self-referent colour preference device was used to study colour preference of the larvae in 24 h. In the survival and development experiment newly hatched zoea I larvae were stocked into 1.4 L plastic culture tanks at an initial density of 100 individual L -1 , fed with Artemia nauplii till they all metamorphosized to juvenile crab. Data indicated that > 60% larvae of every stage had a significant preference to white background (P < .01), followed by red, blue and yellow. The larvae disliked green and black background. Surprisingly, in the survival and development experiment, the best larval performance was found in red and yellow tank (43.89 +/- 2.22% and 42.30 +/- 4.16%), while the larvae in white tank had the lowest final survival rate (19.78 +/- 3.28%) (P < .01). The larvae also showed better synchronization in development in red (19.7 +/- 1.1 d(-1)) and yellow (20.5 +/- 1.2 d(-1)) tank than in black (22.1 +/- 1.8 d(-1)), blue (22.6 +/- 1.3 d(-1)), green (24.1 +/- 1.7 d(-1)) and white tank (24.1 +/- 1.7 d(-1)). The larvae cultured in white tank tended to swim on the bottom of the tank and had pale body colour. The larvae of all stages in blue tank had the highest oxygen consumption rate (P < .05), while those cultured in red and white had the lowest oxygen consumption rate (P < .05). The results indicated that the red and yellow are suitable background colour for larval P. trituberculatus, while white background may become a stressor and should be avoided.