Colour preference of five marine fishes: bias for natural and yellow-dyed krill in laboratory tanks, sea cages and an earthen pond

Abstract

In this study, the colour preference during feeding was determined in three members of the family Sparidae: girella (Girella punctata Gray), the black porgy (Acanthopagrus schlegeli Bleeker) and the Japanese silver bream (Acanthopagrus latus Houttuyn); and in two members of the family Scombridae: the Japanese horse mackerel (Trachurus japonicus Temminck et Schlegel) and the spotted mackerel (Scomber australasicus Cuvier). The three sparids are omnivorous and are confined to neritic habitats and the two scombrids are schooling planktivores and open-ocean forms. The experiments were conducted under three different holding conditions: grey and white tanks in the laboratory, sea cages and an earthen pond. The prey used in the tests was the Antarctic krill, in its natural colour (control) and in artificial colours of yellow, red, green, blue (produced with food dyes) and black (Chinese ink). These prey were offered in different two-colour pairs to groups of fish, and the colour of the krill attacked first was recorded. The frequencies of first attacks against each colour of the different pairs were analysed by the paired-preference test and Thurstone's law of comparative judgment. The data were converted into mean z-scores and significant biases from zero were noted. The five species took without hesitation all the krill of all colours, but preferred blue krill the least, and did not clearly distinguish red from black. The three sparids showed a strong bias for yellow krill under all holding conditions. The two scombrids preferred natural krill and showed poor colour preference. The observed colour preference was probably due to colour per se and may be an innate ability, rather than due to relative brightness (sensitivity of the fish eye), prey conspicuousness (pigmented eyes of the krill), or the associated taste of the dyes.