60 JUNE 2024 • WORLD AQUACULTURE • WWW.WAS.ORG with chloroform and methanol. After drying a kit for cholesterol determination1 was used and measurements were performed in a fluorometer. Besides the statistical analyses of data for growth, protein and lipid content in muscle and hepatopancreas cholesterol levels with one-way ANOVA, we used a model known as broken-line by utilizing weight gain (percent) data. This model helped us to estimate the supplementation requirement. Discussion and Results After 60 days of the feeding trial, the growth performance of juvenile prawns was improved with the inclusion of cholesterol in the diets, as shown in Figure 3. Both growth parameters, the weight gain (WG) and specific growth rate (SGR), of juveniles fed diets with 1.0 and 1.5 g/100g of cholesterol inclusion showed significantly higher values. As mentioned before cholesterol has been related to growth in crustaceans, and it has been shown to be a precursor of molting hormones, the ecdysteroids (Kumar et al. 2018). During molting crustaceans shed their actual exoskeleton and restore a new and bigger one (Mykles 2021), providing the space necessary for growth. By using the WG data with a broken-line model we calculated the requirement and according with the results (Figure 4), the level was 1 g/100 g of diet or 1 percent inclusion. The reported requirements for other species of commercial crustaceans are between 0.2 and 2 percent (Kumar et al. 2018) and our estimated level falls within this range. Related species of Macrobrachium, the giant prawn M. rosenbergii (D´Abramo and Daniels 1994) and the oriental river prawn M. nipponeses (Gu et al. 2017) have estimated dietary requirements of cholesterol of 0.6 percent, and 0.9 percent, respectively. These values are slightly lower than those found in the present work. Apart from species-related factors, other sources of variation that might affect the requirements of cholesterol include the stage of development, feeding rates, and the presence of other nutrients (Kumar et al. 2018). We performed other analyses that allows us to confirm (or not) the result that was obtained with the growth performance. Particularly, the contents of crude protein in muscle (Figure 5) showed higher values in the organisms fed with diets Chol-1.0 and Chol-1.5 although no significant differences were observed with respect of the prawns fed with Chol-0 and Chol-0.5 g. Increasing protein contents in the body when cholesterol is added to diets have previously been observed in other species of Macrobrachium (Gu FIGURE 3. Growth performance, as weight gain and specific growth rate, of juvenile Macrobrachium acanthurus fed different levels of dietary cholesterol. FIGURE 4. Relationship between the weight gain of juvenile Macrobrachium acanthurus and dietary cholesterol level described by the broken-line model. Accordingly, the determined requirement was 1 g/100 g of diet or 1%. FIGURE 5. Contents of protein and lipids in the muscle of juvenile Macrobrachium acanthurus fed different levels of dietary cholesterol. FIGURE 6. Contents of cholesterol in the hepatopancreas of juvenile Macrobrachium acanthurus fed different levels of dietary cholesterol.
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