Fish-Oil-Free Shrimp Diets may Benefit from DHA Additive Inclusion

Adding supplemental DHA to fish-oil-free feeds for farmed\r\nshrimp may improve shrimp growth, and product quality, researchers say.

A team of researchers from institutions in Brazil and Mexico\r\nexplored the use of supplemental DHA (docosahexaenoic acid) and EPA\r\n(eicosapentaenoic acid) in the diets of juvenile Pacific white shrimp. The\r\ngroup published its work in the journal, Aquaculture​​​.

“Since the requirement of DHA in FO [fish oil] free diets\r\nand the finishing diets strategy is still unknown, this study aimed to evaluate\r\nthe growth and FA [fatty acid] profile of marketable size L. vannamei juveniles\r\nusing FO-free diets containing alternative lipid sources and supplemented with\r\nlow DHA levels,” ​the researchers said.

The researchers found that shrimp on the high DHA diet\r\n(H-DHA) demonstrated better growth performance than shrimp on the control diet.\r\nThe level of DHA deposition in muscle tissue reflected the level of the\r\nsupplement in the feed and animals on the H-DHA diet had the largest presence\r\nof the fatty acid.

“To produce FO-free diets due to the foreseen shortage of\r\nFO, for the L. vannamei aquaculture, supplementation with DHA is mandatory,” ​the\r\nresearchers said. “In addition to growth, DHA in shrimp improves the final\r\nproduct to provide high levels of this essential FA to enhance the quality of\r\nconsumers.”​

However, use of the supplement did not alter survival rate,\r\nthey said. And, testing higher levels of the supplement is suggested to find\r\nthe “optimal point of the requirement.”​

Removing fish oil from shrimp diets​

High price, finite supply and varying nutritional content\r\nhave made fishmeal (FM) and fish oil (FO) limiting ingredients when designing\r\ndiets for marine species, the researchers said.

However, marine animals can be “highly dependent”​ on\r\nlong-chain polyunsaturated fatty acids (LC-PUFA) including DHA and EPA, they\r\nsaid. EPA and DHA are common in marine-based feed ingredients like FO and FM.

Several marine algae species also are able to generate meal\r\nand oil with high levels of DHA and PEA and may provide an option to replace FM\r\nand FO in diets, they said.

“Although the algae meal and oil reach higher production\r\ncosts compared to FM and FO, they could be used in low concentrations and\r\nequilibrated using higher proportions of cheaper lipid sources with more stable\r\nproduction (Mourente and Bell, 2006; Glencross, 2009; Turchini et al., 2009),” ​the\r\nresearchers said. “Among those, beef tallow is [a source] used, and its\r\navailability and production cost are promising.​

Why supplement DHA-EPA in shrimp feed?​

The necessary levels of DHA and EPA for diets of several\r\nfarmed marine species have already been established, the researchers said.

However, the required DHA level for Litopenaeus vannamei ​has\r\nnot been found, because the nutrient is not always considered essential as it\r\nwith some fish species, they said. But, previous research reported positive\r\nresults for shrimp growth performance when varying levels of DHA were added to\r\nthe diets for both juvenile shrimp and post-larvae shrimp.

“These differences observed between postlarvae and juveniles\r\nare a piece of evidence to the need for better knowledge on the LC-PUFA\r\nrequirements for this species in different life stages,” ​they said. “Besides,\r\nthe opportunity to produce shrimp at commercial size with an enhance fatty acid\r\nprofile quality for human consumption should be foreseen.”​

In aquaculture, diets have been created to support fish\r\nduring the final growth phase and produce a higher quality final product, the\r\nresearchers said. Adding, “For example, finishing diets for fish are usually\r\nformulated to enhance the LC-PUFA accumulation in the muscle.”​

However, finishing diets are not commonly used in shrimp\r\nproduction unless it is to increase the size of the feed provided, they said.

“Therefore, the use of finishing diets designed with DHA and\r\nEPA supplementation for marketable size L. vannamei juveniles could improve the\r\nquality and performance at this phase, in which the weight gain is naturally\r\nlower,”​ they said.

Feeding trial details​

During the feeding period, 3,000 shrimp received one of four\r\nisoproteic and isolipidic diets designed to include about 410g kg-1 of crude\r\nprotein and 85g kg-1 lipids for a 7-week period, the researchers said.

The diets also had four different levels of a commercially\r\navailable DHA and EPA supplement at 0 (control), 4 (L-DHA), 7 (M-DHA) or 10g\r\nkg-1 (H-DHA), they said. Adding, “The diets resulted with the final DHA\r\nconcentration of 10.7 (Control); 13.1 (L-DHA); 17.0 (M-DHA); and 23.7 mg g−1\r\nlipid (H-DHA).”​

Shrimp were evaluated for weight gain, specific growth rate\r\n(SGR), survival rate and proximate composition, they said. Shrimp tissues also\r\nwere checked for the fatty acid profile.

Results​

Shrimp on all diets had a similar survival rate, the\r\nresearchers said. However, shrimp on the H-DHA diet had a higher final weight\r\ncompared to the control, and shrimp on the M-DHA and H-DHA had an improved\r\nspecific growth rate compared to shrimp on the control and L-DHA diets.

“A linear regression analysis revealed a direct relationship\r\nof dietary DHA levels and final weight,” ​they added.

The level of DHA found in shrimp muscle tissue increased\r\nlinearly as more DHA was added to the diet, the researchers said.

“The results pointed out preferential oxidation of L.\r\nvannamei by FA included in high concentrations in the experimental diets such\r\nas 18:1n-9 and 18:2n-6, those of most representative FA in beef tallow and\r\nsoybean oil composition, respectively,” ​they said. “Inversely, it was observed\r\nan accumulation of essential long-chain polyunsaturated fatty acids (LC-PUFA),\r\nespecially EPA and DHA even at low levels of FA inclusion.”​

No major differences were found in the levels of total\r\nsaturated fatty acid, monounsaturated fatty acid and PUFA based on shrimp diet,\r\nthey said. Although, shrimp on the H-DHA diet had a reduced level of n-6 PUFA\r\ncompared to shrimp receiving the control or L-DHA diets.

“Significant differences were observed in all n-3 PUFA,” ​the\r\nresearchers said. “The concentration of 18:3n-3 was higher in the L-DHA than\r\nthat of M-DHA and H-DHA treatments.”​

\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n

“The EPA level was lower in the L-DHA treatment than that\r\nobtained in the M-DHA, while H-DHA was most representative compared to the\r\nControl and L-DHA treatments, without showing significant differences between\r\nthem,”​ they added.

Source : Feednavigator