Features Research
Dark walls decrease jaw malformation in amberjack

“This study elucidated the phototactic behavior of greater amberjack larvae responding to the brightness of rearing tank walls, inducing walling behavior and jaw malformation,” noted Y. Sawada et al of Kindai University in an abstract entitled, Prevention of jaw malformation in greater amberjack (Seriola Dumerili) by larval rearing with low brightness tank walls.

 As for prevention measures, the results indicated the low brightness rearing tank walls control jaw malformation and improve survival.  It added, however, that low brightness in the upper 30 cm below water surface has limited effect.

For the study three different 80-cm-high rearing tank walls in black, gray and white were used. Monitoring focused on the incidence of jaw malfunction, survival, growth and larval walling behavior.

The latter refers to the behavior of larvae colliding with the tank wall which brings permanent malformation during larval jaw development. 

The results consistently demonstrated that black had the best impact on fish health and behavior, while white had the opposite effect.

The incidence of juvenile malformation was significantly different at 5.8, 22.5 and 26.8 percent for black, gray and white, respectively.

Larval walling behavior was most intensive for white, followed in order by gray and black. Survival rate was significantly higher in black at 12.2%. Meanwhile, gray was at 1.9% and white, 1.4%. 

Another experiment examined the effect of partial brightness of different tank walls on rearing performance in order to study the possibility of “labor-saving “in changing the tank wall color.

Three combinations were used: black-white, from water surface to 30 cm in depth, white-black from 30 to 8-cm in depth and completely black tank wall.

 “Resulting juveniles had the lowest incidence rate of jaw malformation in black-black (31.0%), followed in order by black-white (37.0%) and white-black (44.8%), although these rates were not significantly different (P>0.05),” the researchers noted.

The walling behavior was observed to be more intensive in white-black than the other two wall colors, which were not so different.

 While survival rate was significantly higher (P<0.05) in black-black (13. 6%) than black-white (8.9%) and white-black (2.7%), growth was not different among them.

“Further research is necessary to obtain knowledge on how deep it is necessary to use low brightness color for the tank wall or to explore easier prevention measures,” it was noted.

The study was presented at Aquaculture Europe 2016 held last fall in Edinburgh, Scotland.

 — Ruby Gonzalez