No abstract

A 50-day growth trial was conducted to evaluate the efficacy of Chlorella vulgaris (Beijerinck) as an ingredient in the diets of giant freshwater prawn Macrobrachium rosenbergii (De Man) postlarvae (PL30). Immune response (total haemocyte count and prophenoloxidase activity) was also assessed by subjecting postlarvae to a challenge test against Aeromonas hydrophila (Chester) for 14 days. Isonitrogenous and iso-lipidic test diets were prepared using a fishmeal-based-positive control diet (D0) and four basal diets with inclusion levels of 2% (D2), 4% (D4), 6% (D6) and 8% (D8) C. vulgaris. Postlarvae of M. rosenbergii were randomly stocked (mean initial body weight of 0.19 AE 0.02 g) in 30-L tanks in three replicates per dietary treatment for evaluation of growth performance. Another set of postlarvae (mean initial body weight of 1.25 AE 0.02 g) was randomly distributed in 95-L tanks in three replicates per dietary treatment for the assessment of immune response. Results showed that specific growth rate was significantly higher (P < 0.05) in postlarvae fed D4 and D6. Variations in values for carcass protein, lipid, moisture and ash were also evident. Postlarvae fed diets with Chlorella showed increased prophenol oxidase activity and total haemocyte counts. Moreover, survival rate after challenge with A. hydrophila was significantly increased (P < 0.05). Inclusion of C. vulgaris in diets enhanced immune response and resistance of M. rosenbergii postlarvae against A. hydrophila infection.

A feeding trial was conducted to evaluate the effects of Spirulina (Arthrospira platensis) inclusion in experimental diets of juvenile Nile tilapia (Oreochromis niloticus). Iso-nitrogenous and iso-lipidic diets were prepared using a positive control diet (S0) and four basal diets with A. platensis at 30 % (S30), 45 % (S45), 60 % (S60), and 75 % (S75) inclusion levels. Experimental diets were randomly assigned to tanks (13.35 kg m −3 ) with initial body weight of 0.89±0.02 g in triplicates.The results of the feeding trial demonstrated significantly improved (P < 0.05) growth performance and hepatosomatic and viscerosomatic indices of fish fed S30. Blood chemical profile also indicated desirable values in fish fed A. platensis diets as compared to fish fed S0. On the contrary, fish fed S75 exhibited significantly reduced fish growth. Blood chemical analysis showed significant difference (P<0.05) in levels of plasma triglyceride. Results of the present work indicate that 30 % A. platensis inclusion is deemed the optimal level of dietary replacement for increased growth performance, improved feed utilization efficiency, and enhanced overall health status of Nile tilapia juveniles.

The nutritional value of spirulina in aquafeeds has been studied extensively as a fishmeal replacer or as a functional feed additive to increase growth and health performance of fish in the last decade. Despite increased interest in spirulina research in aquaculture, its increased production cost still limits its use in commercial rations. Zarrouk’s medium is the standard substrate used for growing spirulina. Although this medium offers optimal biomass production, it incurs higher costs due to the expensive components needed for concocting the medium. In this regard, development of cost‐effective alternative culture medium or techniques is necessary for the industrial‐scale production of these microalgae. This paper reviews research on different alternative media for spirulina cultivation and its nutritive value as an aquafeed. Numerous alterations in the composition of Zarrouk’s medium with cheaper chemical ingredients have been explored as a potential substitute for cost‐effective microalgae cultivation. Industrial and processing wastes and by‐products with appropriate nutrient profiles for growing spirulina are also being considered as alternative culture media. The use of rice bran or other cheaper agricultural by‐products, as a cost‐effective growth medium for commercial‐scale spirulina production has yet to be explored extensively in agriculture‐based countries, especially in rice‐producing Asian countries.

A 56-day feeding trial was conducted to determine the effects of supplementing diets of juvenile Japanese flounder, Paralichthys olivaceus, with Eucheuma denticulatum (EDP). Isonitrogenous and isolipidic test diets were prepared using a fishmealbased positive control diet (PC) and a fishmeal-soy protein concentrate negative control diet (NC) supplemented with 3 (D3%), 6 (D6%) and 9% (D9%) EDP. The test diets were assigned to tanks (12 fish tank À1 , initial mean body weight of 0.42 AE 0.01 g) in triplicates. Results of the feeding trial indicated that growth rates and feed efficiency significantly improved (P < 0.05) when 3% EDP was supplemented in the diets. However, there was a significant reduction (P < 0.05) of growth and feed efficiency in fish fed diets with higher supplementation levels. Protein, lipid, dry matter and ash contents of carcass and their corresponding nutrient retention values were not markedly altered in all dietary treatments. Fish fed diets supplemented with EDP exhibited higher (P < 0.05) omega-3 polyunsaturated fatty acid accumulation in dorsal muscle when compared with those of fish fed NC. Blood chemical parameters showed significant differences (P < 0.05) in total cholesterol and triglyceride levels. These results suggest that EDP can be efficiently utilized by Japanese flounder and can promote best growth and feed utilization at a level of 3%.