Early feed restriction may program shrimp for growth

Restricting feed to young shrimp may program shrimp and boost growth performance during the juvenile phase, say researchers.

Photo: ©GettyImages/ vinhdav

An international team of researchers based in Brazil and France explored the potential for feed restriction to establish metabolic programming in shrimp. The group published its work in the journal Aquaculture​​​.

“We hypothesized that a caloric restriction stimulus (a strong environmental driver for the programming in mammals) during the post-larvae stage (i.e., PL1 phase) could improve the use of dietary nutrients in adults,”​ the researchers said. “The purpose of this study was to evaluate the long-term effects of an early stimulus, consisting in a feed restriction (70%) applied at the PL stage, on juvenile shrimp challenged with 3 diets (different protein/carbohydrate ratios) during 70 days.”​

The researchers found that shrimp responded to early feed restriction and that they can be programmed using nutritional stimulus. After the dietary challenge, shrimp were found to have improved growth performance.

“Early feed restriction is associated with modification of gene expression involved in metabolism. ​These data are promising for the advancement of novel nutritional strategies based on programming, including for example the optimization of the development of low protein diets for marine shrimp.”​

Why shrimp metabolic programming?​

Shrimp are a valuable species for aquaculture, the researchers said. However, while farmed shrimp have been spreading, there is a need to find new feeds that are not reliant on wild-caught fish to support future development of the industry.

Fishmeal, although a preferred ingredient has a limited supply and is the most expensive protein source used in shrimp feed, they said. It also can be replaced by other proteins, including animal by-products.

Specific amino acids, fatty acids and minerals need to be supplemented when a fishmeal alternative is used and juvenile whiteleg shrimp need 30-36% digestible protein, they said. “Alternative proteins may contain from 40 to 70% crude protein, but they are often associated with a low nutrient digestibility, unbalanced amino acid profile, anti-nutritional factors, poor attractability and a high carbohydrate content which result in negative effects on growth performance and feed efficiency,”​ they added.

The cheapest element in a shrimp feed can be the carbohydrate (CBH), they said. When added at 20-30% of the diet CBH also serves to spare energy sources from proteins and lipids, but if too much is used the ingredient has been linked to reduced growth and survival.

The idea of nutritional programming has been examined in mammals, the researchers said. The process examines how environmental factors in early development may produce long-term results in physiology and metabolism.

In fish, the process has been explored in rainbow trout, European seabass, Atlantic salmon and zebrafish, they said. However, the process has yet to be explored in crustaceans.

The goal of the study was to evaluate the potential of metabolic programming to alter the use of nutrients needed in diets for whiteleg shrimp, they said. “The best developmental window for the early stimuli was determined previously; indeed, Lage et al. (2017), through mapping key metabolic biomarkers over the early larval development in whiteleg shrimp, suggested that two developmental stages, i.e., protozoea sub-stage 1 Z1 and post-larvae stage PL1, could be the preferential periods to test early stimuli,”​ they added.

Methods and materials​

In the programming phase, 30,000 shrimp at post-larval stage 1 (PL1) were separated among tanks and given a three-day feeding stimulus, the researchers said. During the 3-day feeding stimulus, control group shrimp were given a regular feed allotment, while trial shrimp were given a 70% feed reduction or feed-restricted diet (RES).

After the stimulus period, all shrimp experienced the same conditions for hatchery and nursery phases, a period that lasted 47 days, they said. At that point, juvenile shrimp were moved to 30 rearing tanks for the 70-day dietary challenge.

The 70-day challenge included three separate, extruded feeds, they said.

“A basal diet (P43) was formulated to contain 15.0% fishmeal (% of the diet, as is basis), 43.3% crude protein (CP, dry matter basis, DM) and an NFE (nitrogen-free extract)/CP ratio of 0.7,”​ the researchers said. “Two others diets were designed by replacing fishmeal with wheat flour and soybean meal, so that CP was reduced to 36.9 and 29.6% (diets P37 and P30, respectively) with NFE/CP ratios of 1.0 and 1.5, respectively.”​

Shrimp were collected once a week for measurement and analysis, they said. Final body weight (FBW), specific growth rate (SGR), final survival, gained yield, feed conversion ratio (FCR), apparent feed intake (AFI) were determined.

Results

At the end of the hatchery phase shrimp in both the control and test group had similar survival rates, final body weights and number of post-larvae, the researchers said.

The influence of early feed restriction was checked at the PL4 stage through an examination of mRNA levels for genes involved with digestion, intermediary and energy metabolism, they said. Feed restricted shrimp were similar, save for a down-regulation in the trypsin gene.

After the dietary challenge, AFI and survival rates were found to be the same for all shrimp, however, animals that were initially restricted in diet had improved final body weight and specific growth rate, they said. “Early feed restriction is associated with modification of gene expression involved in metabolism,”​ they added.

Shrimp that received limited feed initially and the P43 or basal diet had the largest final body weight, they said.

“Final body weight, SGR, gained yield and FCR were also significantly modified by the dietary treatments; a better growth performance has been observed when shrimp were fed with the P43 diet (higher protein intake),”​ the researchers said. “By contrast, there was no significant interaction between the early stimulus and the dietary challenge, except for the final body weight.”​

Plasma metabolites were altered for shrimp given the P43 diet, they said. Plasma lactate varied by early stimulus and plasma glucose was increased for shrimp in the RESP43 group, while there was no variation for shrimp in the control group.

There were several differences for mRNA levels of metabolic genes in the hepatopancreas, they said. Two demonstrated an interaction between stimulus and diet – cox VI c and lvglut 1.

“Firstly, the effects of the diets were observed for preamylase, gdh, fbp and pepck gene expressions: mRNA levels for these genes were increased with higher levels of dietary proteins,” ​they said. “Secondly, 8 genes were strongly affected by the early stimulus; decreased mRNA levels for the digestive enzymes (lipase, preamylase, and trypsin), amino acid metabolism (gs), energy metabolism (cox VI b) and glucose metabolism (lvglut 1, lvglut 2 and pk).”  ​

The study was funded by Neovia and LABOMAR’s aquaculture research station.

Source: Aquaculture​

Authors: L Lage, M Serusier, D Weissman, S Putrino, F Baron, A Guyonvarch, M Tournat, A Nunes, S Panserat