Olive flounder farm in Wando County

Dietary effect of low-fishmeal diets on gut microbiota in olive flounder

SOUTH KOREA
Tuesday, April 07, 2020, 05:10 (GMT + 9)

Fish life stage more important modulating intestinal microbiota than diet

The olive flounder (Paralichthys olivaceus) is the most economically important carnivorous marine fish cultured in the Republic of Korea, and accounts for more than 45 percent of all farmed fish production.

Fishmeal remains the gold‐standard protein ingredient for carnivorous aquaculture fish. In olive flounder, a high proportion of fishmeal is generally used to support the growth and health in the juvenile stage, and then it is progressively reduced during the grow‐out stage (~30 to 40 weeks). To reduce the reliance on fishmeal and support the sustainable future development of Korean aquaculture, researchers and producers have worked on cost‐effective alternatives to fishmeal.

View of olive flounder during grow-out at a farm in Korea. Photo by Darryl Jory/aquaculturealliance.org

Many plant proteins have been explored as fishmeal alternatives in aquafeeds, but the presence of some antinutritional factors or nutritional imbalances may negatively affect fish growth, gut microbiota composition, immune response and survival rates.

Gut microbiota are critical to the host’s nutrition, development, immunity, and resistance against stressful conditions. The advent of next‐generation sequencing, NGS [several modern sequencing technologies that allow for sequencing of DNA and RNA much more quickly and cheaply than previously used technologies, and which have transformed the study of molecular biology] enabled more sophisticated analysis of complex gut microbiota by a culture‐independent approach with unprecedented resolution and throughput.

NGS has been used to explore the dietary effects on gut microbiota of different fish species. Most of these studies investigated the dietary effects on fish gut microbiota for a short‐term, but the long‐term dietary effects at different growth stages have generally been overlooked. The dietary effect of plant protein ingredients on gut microbiota of the olive flounder has not been investigated.

The olive flounder (Paralichthys olivaceus) is the most economically important carnivorous marine fish cultured in the Republic of Korea (Photo: aquaculturealliance.org)

This article – adapted and summarized from the original publication [Niu, K-M. et al. 2020. Dietary effect of low fishmeal aquafeed on gut microbiota in olive flounder (Paralichthys olivaceus) at different growth stages. Microbiology Open 9(3), March 2020.] – reported on an investigation of the gut microbiota of olive flounder at different growth stages with long‐term dietary administration of plant‐based low fishmeal and practical fishmeal diets by a culture‐independent metagenomic [permitting comparisons of genetic material from multiple samples] approach.

Study setup

We formulated and tested two isonitrogenous and isolipidic diets as a fishmeal (FM)-based control diet (Con) and a plant protein-based low-FM diet (FM30) with 30 percent fishmeal replacement using soybean meal, corn gluten meal and corn concentrate. The two diets were produced by thoroughly mixing the feed ingredients, followed by extrusion. The pellets were then air-dried at 60 degrees-C for three hours and stored at minus-20 degrees-C until use.

The feeding trial was conducted at Aquafeed Research Center (Pohang), National Institute of Fisheries Science (NIFS), Republic of Korea. Juvenile olive flounder (average initial body weight, 30 grams) were obtained from the Korea NIFS and acclimated to environmental conditions for eight weeks while fed with the Con diet prior to the experiment.

The fish were reared in an indoor flow-through system with standard conditions, and the water temperature ranged from 16.8 to 26.1 degrees-C. After acclimation, 300 fish in each treatment fed with the Con or FM30 diet were randomly distributed into three polyvinyl circular tanks (100 fish/tank; volume, 400 liters) supplied with seawater at a flow rate of 20 liters per minute and aeration.

The feeding trial was conducted for eight months, and all the fish were fed twice a day ad libitum. Three fish, under 100 grams, were collected before the initiation of the experiment and designated the juvenile stage (<100 grams). Fish sampled during the study were designated as the grower (~400 grams), subadult (~800 grams) and adult (>1,000 grams) growth stages based on their body weight and length (Fig. 1).

Fig. 1: Growth stage and diet‐based gut bacterial community in olive flounder: (a) Schematic representation for the overall study; Con, a fishmeal-based control diet; FM30, a low fishmeal diet containing a blend of plant proteins replacing 30 percent of fishmeal (FM30); (b) average body weight (BW) and length (BL) of the used fish samples.

For detailed information on experimental design and diets, fish and study conditions; sample collection, DNA extraction and sequencing; sequencing data analysis; and statistical analyses, refer to the original publication.

Author: Dr. Soo Ki Kim (This article has 10 co-authors but only the affiliation information for one of the corresponding authors) | Global Aquaculture Advocate | Read the complete article here

This study was supported by a grant from the National Institute of Fisheries Science (R2019012), Republic of Korea

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