The present study evaluated the effects of supplemental dietary α-linolenic acid (ALA, 18:3n-3) on growth performance, body composition, hepatic fat metabolizing enzymes, and fatty acid profiles of coho salmon (Oncorhynchus kisutch) alevins cultured in freshwater. Six isonitrogenous and isolipidic experimental diets were formulated to attain different levels of ALA (0.09, 0.41, 0.76, 1.03, 1.32, and 1.68% dry weight) by adding linseed oil in a basal diet, respectively. Each diet was fed to triplicate groups of alevins (50 fish in each tank) with initial mean body weight of 0.352 ± 0.002 g. Fish were reared in a freshwater flow-through rearing system and fed to apparent satiation 4 times daily for 12 weeks. The specific growth rate (SGR) increased with increasing dietary ALA level, which reached the peak at 1.03% ALA group ( ). The final body weight (FBW) and SGR showed linear, quadratic, and cubic responses with the dietary ALA level. The whole-body crude protein increased with increasing dietary ALA level while lipid content was the opposite trend ( ). However, the content of crude lipid in the whole-body of fish showed quadratic and cubic responses with the dietary ALA level. In addition, except for fatty acid synthase (FAS), the hepatic enzymes activities of lipoprotein lipase (LPL), hepatic lipase (HL), and malate dehydrogenase (MDH) showed linear, quadratic, and cubic response with the dietary ALA level ( ) The activities of hepatic LPL and HL in 1.32% ALA group were significantly higher than other groups ( ). The activities of hepatic MDH and FAS in 1.32% ALA group were the lowest, which were significantly lower than those in ALA groups (form 0.09% to1.03%) ( ). Except for the content of MUFA, the contents of other fatty acids showed linear, quadratic, and cubic response with the dietary ALA level. The ALA and ∑n-3 PUFA content significantly increased with increasing dietary ALA levels ( ). These results indicated that dietary ALA actively impacted fish growth performance, hepatic lipid metabolizing enzymes, and muscle fatty acid profile. The cubic regression analysis based on SGR as evaluation indices indicated that the optimal dietary ALA content was 1.33% dry weight of diet for alevins.

Enzymatic chicken pulp (ECP) is an animal protein source that has been proven to be of excellent nutritional content and good quality for the majority of aquatic organisms because of its quality protein, small peptides, palatability, vitamins, and minerals. An 8-week nutritional trial was conducted to assess the effects of an ECP-based diet on the growth performance, digestive enzyme activity, and gene mRNA expression of Pacific white shrimp (Litopenaeus vannamei). Fish soluble pulp (FSP) served as the control group while in the experimental groups, and ECPs with three protein contents were used to replace FSP in equal amounts, named ECP1, ECP2, and ECP3, respectively. No significant difference in weight gain rate, specific growth rate, survival rate, or feed conversion ratio was observed (p > 0.05) between the groups. Ash content in the Pacific shrimp’s whole body was significantly higher in the ECP1 and ECP3 groups compared to the other groups (p < 0.05). Intestinal amylase and protease activities were the highest in the ECP1 and ECP2 groups, respectively (p < 0.05). With respect to gene mRNA expression, neuropeptide Y, excitatory amino acid transporter, and fatty acid transport protein 4 were significantly high in the ECP1 group (p < 0.05). In conclusion, these three ECPs have their advantages to replace FSP in shrimp feed, but ECP1 is more effective if the effects of digestive enzyme activity, appetite, and expression of growth-related genes are considered.

Copper (Cu) is an essential trace mineral for the growth of most farmed fish species. Since natural water typically contains low Cu levels, exogenous Cu supplementation may be required in intensive aquaculture systems to meet the nutritional requirements of certain fish species. A 10-week feeding experiment was conducted to evaluate the Cu requirement on growth performance, tissue Cu content, hematological parameters and anti-oxidant responses in coho salmon Oncorhynchus kisutch (Walbaum, 1792). In this experiment, six experimental diets supplemented with graded Cu (CuSO₄ used as Cu source) contents (0.20, 2.10, 3.70, 5.80, 7.75, and 9.85 mg/kg) to feed the fish (180.22 ± 0.41 g). Total 180 fish were randomly distributed across 18 individuals tank (10 fish/cage, water volume 1,000-L) fed three times a day. The result showed that the mortality and morphological indices were completely unaffected by the increasing Cu supplementation in the diet (P > 0.05). Whereas, the non-supplemented diet (0.20 mg Cu/kg) had a poor growth performance of the fish (P < 0.05), including the lowest final body weight and specific growth rate, the highest feed conversion ratio. No significant differences (P > 0.05) were observed in the proximate composition of muscle across graded dietary copper levels. However, increasing dietary Cu level induced Cu accumulation (P < 0.05), but higher Cu level in the diet (> 5.8 mg/kg) did not further increase of muscle and liver in coho salmon. Compared with the 0.20 Cu mg/kg in diet, the supplemented diet enhanced the antioxidant capacity in liver and serum, and decrease the content of malondialdehyde in liver (P < 0.05). Diet with 0.20-5.80 mg/kg supplemental Cu significantly increased the serum alkaline phosphatase and lysozyme activities, decrease the serum alanine aminotransferase and aspartate aminotransferase activities (P < 0.05), while higher dietary Cu level (> 5.8 mg/kg) showed the opposite trend. The broken-line analysis based on specific growth rate, liver Cu accumulation, copper-zinc superoxide dismutase in liver and serum, the appropriate dietary Cu level for coho salmon were estimated to be 5.29–5.92 mg/kg.