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The live feed that could revolutionise grouper aquaculture

The growth of grouper aquaculture has been held back by the difficulties experienced in the larval rearing stage. However, according to CFEED, the use of copepods at the first feeding stage is leading to marked improvements in production.

26 November 2020, at 7:58am

Groupers are highly prized throughout Asia and have traditionally been caught using nets, traps and baited hooks, but overfishing has led to diminishing wild stocks all over the world. As a result, over the last decade there has been a concerted effort to develop the means to culture grouper – both to help relieve pressure on wild stocks and to provide regular quantities of high-quality fish to the market (Frisch, Cameron, Williamson, & Williams, 2016) (Rimmer & Glamuzina, 2019).

Giant grouper swimming near a coral reef
Grouper is becoming a more popular aquaculture offering across Asia

One of the key constraints limiting growth of the grouper aquaculture industry is a lack of high-quality fingerlings. This problem is due to two main issues – the limited availability of good quality eggs, and the extremely small size of the newly hatched grouper larvae. Recent developments on cryopreservation techniques for storing tiger grouper sperm in Vietnam could help address the first issue. As for the second, the small size renders the grouper larvae fragile and in need of small live prey of adequate nutritional value.

Where rotifers fall short

While today’s practice of feeding rotifers during the first larval period has allowed for cultivation of various grouper species, the survival rate is usually low and the growth and quality of the larvae varied. To ensure the rotifers have an adequate nutrient composition is not straightforward – they often lack key nutrients such as taurine, vitamin A, Iodine and fatty acids like DHA and EPA. Looking into alternative feed solutions has therefore been a priority.

Pictures of tiger grouper larvae, showing the difference in growth rates depending on feed
Picture of a nine-day-old tiger grouper larvae (E. fuscoguttatus) from a hatchery in Thailand. The left one was fed copepods of Acartia tonsa in addition to rotifers, while only rotifers were fed to the one on the right. The pictures are taken at the same magnification.

© CFEED

In the wake of this, several studies have appeared showcasing the potential offered by the application of copepods as feeds for larval grouper. For larval leopard coral grouper (Plectropomus leopardus) a tenfold increase in survival, in addition to more rapid development, was observed (Burgess, Callan, Touse, & Santos, 2019) (Melianawati, Astuni, & Suwirya, 2013). Adding copepods to the diet also quadrupled the survival rate of tiger grouper (Epinephelus fuscoguttatus) (Rimmer, et al., 2011). In addition, growth parameters such as total length, body depth and dorsal and pelvic spine length were positively affected, all in all producing more vigorous larvae.

Despite these results, setting up copepod production units has not been an option for most hatcheries, as they require much work and don’t always produce a steady supply. However, due to companies like CFEED* now supplying the Asian market, copepod eggs can be obtained and hatched on demand in a similar way as Artemia cysts. The newly hatched copepod nauplii are just below 100 µm in length, making them an ideal size for the young grouper larvae. This has led to a number of commercial hatcheries starting to incorporate copepods into their feeds. One of these, Eco Aquaculture Asia in Thailand, reported that including copepods in their hatchery feeds had led to stronger and faster growing grouper fry being produced, ultimately helping to increase their production levels.

The nutritional benefits of copepods

One benefit from feeding copepods comes from their capacity to stimulate enzyme activity in the gut of the grouper larvae. For tiger grouper a significant increase in enzymatic (protease) response was demonstrated when copepod nauplii were added to the diet, raising the enzyme activity by 25.8 percent compared to traditional live feeds such as rotifers and Artemia (Rimmer, et al., 2011). Even the addition of a small proportion of copepods was sufficient to stimulate this increase. A similar result was seen for larval coral trout, where both a full and a partial inclusion of copepods increased the activity of the digestive enzymes protease, amylase and lipase significantly (Melianawati, Pratiwi, Puniawati, & Astuti, 2015).

Graph illustrating the enzyme response to adding copepods to tiger grouper diets from two days after hatch onwards
Enzymic (protease) response to the addition of copepods in the diet for early tiger grouper (E. fuscoguttatus). The copepods were added at the given densities as a single addition at two days post-hatch. No further addition of copepods was made, but rotifers were added daily to maintain the live feed density.

© Rimmer, et al., 2011

Another factor seen to be important for grouper larvae is the fatty acid composition of the live prey. In addition to ARA and EPA, the fatty acid DHA has been identified to be of crucial importance for tiger grouper larvae (Rimmer, et al., 2011). When starved, the larvae conserve this to a higher degree than other fatty acids, indicating how essential it is for early larval growth and development.

This could provide another reason why copepods boost survival, growth and development of grouper larvae, as they naturally contain high level of these fatty acids, commonly reaching over 25 percent of the total lipid content (van der Meeren, Olsen, Hamre, & Fyhn, 2008). They are also known to have a naturally high content of taurine, astaxanthin, vitamin C and iodine, and contain 60-70 percent protein.

Picture of newly-hatched nauplii, a type of copepod used to feed juvenile marine finfish
The newly hatched nauplii of Acartia tonsa are close to 100 µm in length, making them perfect as a feed for the larvae of most grouper species.

© CFEED

In nature, copepods are considered the most important group of zooplankton, forming a vital link between primary production and fish larvae. Studies on gut content in larvae of coastal tropical fish revealed that the majority relied on copepods as their primary source of feed (Sampey, Mckinnon, Meekan, & Mccormick, 2007).

Providing a way for fish producers to offer their fish larvae the diet they would prefer in the wild has been one of the goals for the Norwegian based company CFEED. With bio-secure, indoor production of the calanoid copepod Acartia tonsa, they can provide a stable, commercial supply of copepod eggs to hatcheries around the world. These eggs can be hatched on demand, providing a nutritionally balanced prey option for the fish larvae. The small size of the newly hatched nauplii makes them ideal feeds during the most sensitive stage for the grouper larvae. In combination with a nutritional composition that is ideal for first feeding, this easy solution of introducing copepods into commercial grouper aquaculture could greatly improve the productivity of hatcheries in the future.

*The Fish Site is owned by Hatch, which has invested in CFEED, but we remain editorially independent.

References
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Burgess, A. I., Callan, C. K., Touse, R., & Santos, M. D. (2019) Increasing survival an growth in larval leopard coral grouper (Plectropomus leopardus) using intensively cultured Parvocalanus crassirostris nauplii. Journal of the World Aquaculture Society
Douglas, I. (2020) Thailand grouper farm sticks to its sustainable roots. Hatchery International
Frisch, A. J., Cameron, D., Williamson, D. H., & Williams, A. J. (2016) Key aspects of the biology, fisheries and management of Coral grouper. Reviews in Fish Biology and Fisheries
Melianawati, R., Astuni, N. W., & Suwirya, K. (2013) The use of copepods to improve juveniles production of coral trout Plectropomus leopardus (Lacepède, 1802). Middle-East Journal of Scientific Research, 237-244
Melianawati, R., Pratiwi, R., Puniawati, N., & Astuti, P. (2015) The effect of various kind of live feeds to digestive enzymes activity of coral trout Plectropomus leopardus (Lacepède, 1802) larvae. International Journal of Fisheries and Aquatic Studies, 83-88
Rimmer, M. A., & Glamuzina, B. (2019) A review of grouper (Family Serranidae: Subfamily Epinephelinae) aquaculture from a sustainability science perspective. Reviews in Aquaculture, 58-87
Rimmer, M. A., Williams, K., Giri, N. A., Knuckey, R., Reynolds, A., Marte, C., ..., Luu, L. T. (2011) Improved hatchery and grow-out technology for marine finfish aquaculture in the Asia-Pacific region. Canberra: Australian Centre for International Agriculture Research
Sampey, A., Mckinnon, A. D., Meekan, M. G., & Mccormick, M. I. (2007) Glimpse into guts: Overview of the feeding of larvae of tropical shorefishes. Marine Ecology Progress Series, 243-257
van Beijnen, J., & Yan, G. (2018) Super grouper: advances in RAS production in Asia. The Fish Site
van der Meeren, T., Olsen, R. E., Hamre, K., & Fyhn, H. J. (2008) Biochemical composition of copepods for evaluation of feed quality in production of juvenile marine fish. Aquaculture, 375-397

CFEED

Maren Gagnat has spent the last decade on optimising live feed production and larval feeding regimes for various cold-water and warm-water marine species. In her position at CFEED she is working together with hatcheries worldwide, identifying when and how to incorporate copepods and which benefits that arise from it.

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