Association Between the Blue Color Intensity of the Skin with Growth Performance and Skin Spottiness in a Blue-Colored Strain of Rainbow Trout (Oncorhynchus mykiss)

Blue-colored phenotypes have the potential to enhance the external appearance of rainbow trout for marketing due to their attractive skin coloration. However, further analyses are necessary to assess their overall performance for fish farming purposes.

To investigate a blue-colored strain of rainbow trout in order to determine whether growth performance and spotting variation of the skin, either in number or size, are related to Blue Color Intensity on the back skin (BCI).

A correlation analysis and comparisons among trout separated into Low- and High-BCI categories were carried out in three blue-colored groups of rainbow trout.

In all groups, BCI was significantly and positively related to body weight (0.01 < P < 0.05). There was a significant and negative association between BCI and the number of dark spots in one group (P < 0.001), whereas no significant association was observed among BCI and dark spot size in any of the groups (P > 0.05). In one group, a significantly higher body weight (P < 0.05) was observed in the High-BCI (BCI ≥ 50%) than in the Low-BCI (BCI < 50%) category. The same pattern was observed in two groups (P < 0.05) when the lowest (1st) and highest (4^th) quartiles of BCI were compared. In one group, number of dark spots was significantly lower in the High-BCI (≥ 50% and 4^th quartile) than in the Low-BCI (< 50% and 1st quartile) category (P < 0.01 and P < 0.05, respectively). Dark spot size presented no significant differences among BCI categories (P > 0.05) in any of the groups.

Results suggest that trout with more intensely blue colored skin has better growth performance and relatively less spotted skin than less intensely blue-colored specimens. These characteristics may represent an interesting advantage for using this class of trout in intensive fish farming.