Manganese is an essential metal for fish and requirements have been established for several finfish but not for gilthead seabream. A team of researchers, together with Skretting, aimed to establish the optimal dietary supplementation level of this mineral in gilthead seabream fingerlings fed plant-based diets.
Gilthead seabream fingerlings were fed five practical diets high in vegetable ingredients (fishmeal: 10%, fish oil: 6%). The diets were supplemented to contain 19, 27, 30, 41 and 66 mg Mn kg−1 as MnSO4. Four hundred and fifty seabream fingerlings were randomly distributed in 15 tanks and fed one of the five diets until apparent satiation three times per day for 42 days. Growth parameters including feed intake, thermal growth coefficient and feed conversion ratio were calculated.
After the feeding trial, fish almost tripled their weight, but dietary manganese levels did not affect growth parameters or survival. The high fishmeal substitution levels led to high manganese contents in the basal diet (19 mg Mn kg−1 diet), which seemed to be sufficient to promote seabream growth. Body lipid composition, protein and ash were not affected by the dietary manganese. Similarly, whole-body, liver and vertebrae mineral contents were not affected by manganese supplementation. Morphological characteristics of the liver had no significant differences among dietary manganese levels. However, an increase of manganese contents beyond 30 mg Mn kg−1 down-regulated MnSOD expression.
“Overall, results suggest that the manganese content present in the basal diet (19 mg Mn kg−1) was sufficient to cover the requirements in juvenile gilthead seabream fed practical plant-based diets, although results from oxidative status markers might point out the need to increase supplementation levels beyond this point when fish are under conditions that may affect their oxidative status,” researchers concluded.
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