No significant effect of additive ratios of docosahexaenoic acid to eicosapentaenoic acid on the survival and growth of cobia (Rachycentron canadum) juvenile

Abstract

An experiment was conducted in the laboratory to investigate the effects of additive ratios of docosahexaenoic acid (DHA) to eicosapentaenoic acid (EPA) on the growth and survival of cobia (Rachycentron canadum) juveniles from August to October 2005. Three hundred and eighty cobia juveniles (56 days of age, body weight 6.9 ± 0.1 g, body length 9.2 ± 0.1 cm) were selected and 20 of them were freely taken for initial sample analysis in the week 0. Additional 360 juveniles were randomly assigned into eight groups with triplicate, total 24 tanks with 15 fish each. Cobia juveniles were reared in glass‐steel tanks (200‐L volume per tank) using filtered seawater with temperature 26–30.5 °C, salinity 25.4–33.0 g L−1 and pH 7.8–8.0. Cobia juveniles were fed for 8 weeks using seven treatment diets (D‐1 to D‐7) with the same amount of DHA and EPA (15.0 ± 1.2 g kg−1 of dried diet), but varying ratios of DHA to EPA (0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, respectively) and a control diet (D‐0, DHA + EPA = 8.0 g kg−1 of dried diet, DHA/EPA = 1.3). Five juveniles per tank were randomly taken for sample analysis at the end of weeks 4 and 8, respectively. The highest protein efficiency rate (PER; 1.5 in mean), average body weight (BW; 73.3 g per fish in mean) and the lowest feed conversion ratio (FCR; 1.6 in mean) were obtained in cobia juveniles fed the control diet at the end of week 8. These parameters were significantly different (P < 0.05) among juveniles fed the control and treatment diets; however, no significant difference (P > 0.05) was found among juveniles fed the treatment diets evaluated in this study. It was concluded that the survival and growth of cobia juveniles were not greatly influenced by additive ratios of DHA to EPA in our experimental conditions.

Fish oil replacement by soybean oil in the diet of fat snook juveniles

“…A similar finding was reported for Dicentrarchus labrax, in an experiment by which fish received the same amount of fishmeal, and fish oil source was replaced by soybean oil (Hunt & Tekelioglu, 2008). Similar results were also shown for Rachycentron canadum, for which the higher amounts of diet-supplementation with EPA and DHA than those already present in fishmeal did not improve fish performance (Ding et al, 2009).…”

“…The lack of long-chain fatty acids in vegetal oils might have been overcome by the diet formulated with 52% marine fishmeal, which provided about 2.5‰ EPA and 5.4‰ DHA to the diet. These values are close to the ones used in feed formulas distributed to other marine species (Peng et al, 2008;Ding et al, 2009), suggesting that, depending on the diet composition, supplementation with EPA and DHA might be unnecessary to feed juveniles of fat snook. Similar results have also been reported for Solea senegalensis (Borges et al, 2014).…”

“…Polyunsaturated fatty acids supplementation has been shown as unnecessary in the developmental phase for other species, and the substitution of fish oil by vegetable oil does not affect fish performance and growth (Hunt & Tekelioglu, 2008;Ding et al, 2009;Borges et al, 2014).…”

Dietary docosahexaenoic acid to eicosapentaenoic acid (DHA/EPA) ratio influenced growth performance, immune response, stress resistance and tissue fatty acid composition of juvenile Japanese seabass,Lateolabrax japonicus(Cuvier)

“…A study on cobia (Ding et al . ) showed that the growth of juvenile cobia was not greatly influenced by ratios of DHA to EPA since a high content of dietary fishmeal (67%) used in the study probably have met the requirement of n‐3 LC‐PUFAs in cobia and masked the effects of the additive DHA and EPA.…”

“…This made the present study more worthwhile for the farmers since the difference between DHA and EPA in their effects on fish was always species‐specific and easily influenced by rearing conditions (Koven, Tandler, Sklan & Kissil ; Tago et al . ; Villalta & Estévez ; Ding, Xu, Zhang, Wang, Chen & Sun ; Dantagnan et al . ; Trushenski et al .…”