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A 60-day growth experiment was conducted to investigate the effect of dietary replacement of fishmeal by Spirulina platensis on growth performance, digestion and physiological parameters in juvenile gibel carp (5.0 AE 1.0 g). Four diets were formulated to replace 0 (SP0), 50% (SP50), 75% (SP75) and 100% (SP100) of dietary fishmeal protein by S. platensis respectively. Other two diets based on SP100 were supplemented with 2% dicalcium phosphate (SP100 + P) or 0.28% coated lysine (SP100 + Lys). The results showed that no significant differences of specific growth rate (SGR), feed efficiency (FE), feeding rate (FR) and protein efficiency ratio (PER) were observed between SP0 group and the replacement groups (SP50, SP75 and SP100). FE and PER of fish-fed SP100 + Lys diet were significantly higher than the fish-fed SP100 diet (p < .05). Apparent digestibility coefficients (ADCs) of dry matter, protein, energy and phosphorus increased significantly with the increasing S. platensis inclusion. Meanwhile, fish from SP100 + P or SP100 + Lys group had higher ADCs of nutrients compared to the SP100 group (p < .05). Compared with SP0 diet, fish-fed S. platensis diets had higher activities of plasma superoxide dismutase, hepatopancreas total antioxidant capacity, plasma alkaline phosphatase and plasma lysozyme, as well as the lower content of plasma malondialdehyde. The present results indicated that dietary fishmeal could be fully replaced by S. platensis without any negative effects on growth performance of gibel carp. Supplementation of lysine in the S. platensis replacement diet could further improve the feed utilization of gibel carp. K E Y W O R D Sdigestibility, gibel carp, growth performance, protein replacement, Spirulina platensis | INTRODUCTIONAs the traditional protein source in aquafeeds, fishmeal gets extensive use for its high contents of essential amino acids, essential fatty acids, mineral elements, bioactive substance and low level of anti-nutritional factors (Hardy, 2010). With the development of aquafeeds industry, the demands for fishmeal and fish oil are still rising (FAO, 2012). Although the worldwide fishmeal production has obtained a relatively high and stable level, even some of which are acquired through overfishing, the production still could not match

In recent decades, due to the continuous increasing demand for aquatic products, the global fishery industry has been expanding rapidly, and aquaculture output has been increasing at an unprecedented speed (Cole et al., 2009). High-density aquaculture is the current mainstream aquaculture modes worldwide. While the environmental stress induced by high rearing density results in poor resistance to disease and vulnerability to infection by pathogenic microorganisms in fish (Costas, Aragão, Mancera, Dinis, & Conceicão, 2008). For a long time, many antibiotics and chemotherapeutic agents have been used to improve non-specific immunity and to treat some bacterial infections in aquatic animals, but these agents also lead to undesirable effects, such as antibiotic resistance, pharmaceutical bioaccumulation and environmental pollution (Bilen, Bulut, & Bilen, 2011;Harikrishnan, Balasundaram, & Heo, 2011). In recent years, many harmless therapeutic techniques and

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An eight-week experiment was undertaken to examine the effect of dietary hydroxyproline (Hyp) supplementation on growth performance, collagen synthesis, muscle quality of an improved triploid crucian carp (Carassius auratus Triploid) (ITCC). Six isonitrogenous (340 g/kg diet), isolipidic (60 g/kg diet) and isocaloric (17.80 MJ/kg diet) diets were formulated containing a certain amount of Hyp: 0.09% (the control group), 0.39, 0.76, 1.14, 1.53 and 1.90%. Each diet was randomly assigned to three tanks and each group was fed two times daily until apparent satiation. The results showed that growth performance and feed utilization of ITCC were significantly improved with the dietary Hyp level was increased from 0.09 to 0.76%. Crude protein, threonine and arginine content in the dorsal muscle in 0.76% hydroxyproline group were significantly higher than those in basic diet group (p &lt; 0.05). The muscle textural characteristics increased remarkably with the amount of Hyp in the diet rising from 0.09 to 1.53% (p &lt; 0.05). Meanwhile, the contents of type I collagen (Col I) and Pyridinium crosslink (PYD) in the muscle of fish were significantly increased by dietary Hyp (p &lt; 0.05). The muscle fiber diameter and density of the fish were significantly increased when fed with 0.76% Hyp (p &lt; 0.05). Furthermore, dietary supplementation with an appropriate concentration of Hyp substantially increased the expression of genes involved in collagen synthesis (col1a1, col1a2, p4hα1, p4hβ, smad4, smad5, smad9, and tgf-β) and muscle growth (igf-1, tor, myod, myf5, and myhc) (p &lt; 0.05). In conclusion, dietary supplementation of Hyp can enhance fish growth performance, collagen production, muscle textural characteristics and muscle growth of ITCC. According to the SGR broken-line analysis, the recommended supplementation level of Hyp was 0.74% in the diet for ITCC, corresponding to 2.2% of dietary protein.