For omnivorous crayfish, plant raw materials can be good alternatives to dietary fish meal for the Redclaw crayfish Cherax quadricarinatus. A 56-day feeding trial was conducted in C. quadricarinatus (11.70 ± 0.13 g) fed with eight diets. Diet with 100% fish meal (FM) as the protein source was the control. Seven experimental diets were formulated by replacing 75% or 100% of FM with soybean meal (SM75, SM100) or cottonseed meal (CM75 and CM100), and a mixture of SM and CM (protein content is 1:1) replacing 50%, 75% or 100% of FM (SC50, SC75, and SC100). Crayfish fed the CM100 and SC100 showed significantly lower WG, SGR, trypsin and pepsin activities compared to control diet. Crayfish in CM100 group showed significantly higher GPx, ALT, AST activities and MDA content than the control. SM100 and CM100 diets can cause slight separation of the peritrophic membrane from the intestinal folds. The pepsin activity of crayfish in SC50 were significantly higher than those in other experimental diets. The highest WG and muscle arginine content were also found in crayfish fed SC50. The relative abundance of Proteobacteria phylum, Unclassified Enterobacteriaceae, and Candidatus Bacilloplasma was significantly higher, but the relative abundance of Actinobacteriota phylum was significantly lower in crayfish fed SM100, CM100, and SC100 than those in control. Microbiota functional prediction indicated that the relative abundance of “cell motility” pathway in crayfish fed CM100 was significantly decreased compared to control. In conclusion, only half of the fish meal can be effective substituted with a mixture of soybean meal and cottonseed meal (protein content is 1:1) for C. quadricarinatus.
The optimal supplementation of lipid nutrients in the diet showed crucial physiological functions in gonadal development and maturation in adult female aquatic animals. Four isonitrogenous and isolipidic diets with no extra lecithin supplementation (control), 2% soybean lecithin (SL), egg yolk lecithin (EL), or krill oil (KO) supplementation were formulated for Cherax quadricarinatus (
72.32
±
3.58
g
). Ovary development and physiological characteristics of crayfish were evaluated after a 10-week feeding trial. The results indicated that SL, EL, or KO supplementation all significantly increased the gonadosomatic index, especially in the KO group. Crayfish fed the diet with SL showed the highest hepatosomatic index compared with those fed the other experimental diets. KO was more efficient than SL and EL in promoting triacylglycerol and cholesterol deposition in the ovary and hepatopancreas but also showed the lowest concentration of low-density lipoprotein cholesterol in the serum. KO significantly increased yolk granule deposition and accelerated oocyte maturation than other experimental groups. Furthermore, dietary phospholipids significantly enhanced the gonad-stimulating hormone concentration in the ovary and reduced the secretion of gonad-inhibiting hormones in the eyestalk. KO supplementation also significantly improved organic antioxidant capacity. From the ovarian lipidomics results, phosphatidylcholine and phosphatidylethanolamine are two main glycerophospholipids that respond to different dietary phospholipids. Polyunsaturated fatty acids (especially C18:2n-6, C18:3n-3, C20:4n-6, C20:5n-3, and C22:6n-3) were pivotal participants during ovarian development of crayfish regardless of lipid type. Combined with the ovarian transcriptome, the best positive function of KO was due to activated steroid hormone biosynthesis, sphingolipid signaling, retinol metabolism, lipolysis, starch and sucrose metabolism, vitamin digestion and absorption, and pancreatic secretion. As a consequence, dietary supplementation with SL, EL, or KO all improved the ovarian development quality of C. quadricarinatus, especially KO, which was the optimum choice for promoting ovary development in adult female C. quadricarinatus.
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