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Reliance on marine resources is an ongoing constraint in aquaculture nutrition, and progress in identifying alternative ingredients is becoming increasingly marginal.
Carnivorous fishes, such as the Walleye Sander vitreus, are nutritionally demanding for fish meal. A promising alternative to marine‐origin fish meal, the supply of which has been stagnant in recent decades, is fish meal derived from undesirable freshwater species, such as the White Sucker Catostomus commersonii. To evaluate the relative value of such ingredients, we examined the growth performance of Walleye juveniles. Two dietary treatments were tested: an experimental (EXP) diet that was manufactured using White Sucker as fish meal in comparison with a commercial (COM) diet, EWOS Micro (EWOS Canada, Ltd.). Dietary lipid content was 15.1% and 16.8% for EXP and COM diets, respectively. The protein content was 50.4% and 57.6% for EXP and COM diets, respectively. The energy content was 5,098.76 ± 9.23 cal/g (mean ± SD) for the EXP diet and 5,134.47 ± 10.95 cal/g for the COM diet. Starting at 27 d posthatch, Walleye juveniles (initial weight [mean ± SD] = 0.030 ± 0.008 g; initial length = 15.7 ± 1.5 mm) were reared for 6 weeks in three replicate tanks for each treatment. Condition factor (0.83), final weight (1.12 ± 0.30 g), and weight gain (1.09 ± 0.06 g) were higher in fish that were fed the EXP diet. Similarly, the energetic lipid content of fish in the EXP treatment group (mean ± SD = 5.01 ± 0.45 g/kg) was also higher than that of fish fed the COM diet (3.30 ± 0.53 g/kg). Although the polar lipid content (membrane lipids) was similar in fish from the two treatments, the nutritional ratio for COM juveniles was over 1.5 for arachidonic acid and docosahexaenoic acid, indicating selective incorporation by juveniles and suggesting a potential dietary imbalance of these fatty acids. Furthermore, the higher observed selective incorporation of oleic acid in juveniles fed the EXP diet suggested that a higher value of this fatty acid in the EXP feed could have increased Walleye growth performance. Threonine was the main essential amino acid (AA; >18.5% of total AAs), while serine and glycine contributed the highest percentages of the nonessential AAs (>31.0% and 8.5% of total AAs, respectively). All three AAs, often considered limiting ingredients, are important to support growth and are involved in metabolic processes in some fish species. Our results demonstrate that feed pellets made with White Sucker fish meal improved growth in Walleye juveniles and can serve as a suitable and probably lower‐cost regional alternative to marine fish meal in feeds for carnivorous fishes. [Image credit: Jean‐luc Lacroix]
