5 March 2019 – Humanity’s hunger for fish means a promising future for the aquaculture industry. However, in some respects, the sector is still in its infancy compared to terrestrial agriculture, and its rapid expansion may be checked by the need to work through certain technical hurdles. One such chokepoint, experts agree, is likely to be the availability of live feed, namely Artemia, for use in fish and shrimp hatcheries.

Constraints which oblige the use of live feed in aqua hatcheries

The feeding of newly born or hatched individuals of any species is delicate, but in many aquatic species, there are several unique complexities to factor in, including mobility and development levels. Fish fry who have only just transitioned from a yolk sac often require their food to be in the water column, rather than settled on the bottom; moreover, many fish larvae may simply not react to inert particles of feed even if suspended in the water column, instead feeding when stimulated by the movement of live prey. Furthermore, they often have an extremely rudimentary digestive system, in some cases using the digestive enzymes of the organism they are consuming in order to digest that organism—in the words of Dr. Michael Schwarz, director of the Virginia Seafood Agricultural Research and Extension Center at Virginia Tech, “it’s a trigger for the enzymatic system in the fish.” Finally, they are often only able to handle feed of up to a few microns in size.

Current standard practice generally requires the use of live feeds during these stages of life, at least for most marine finfish with a comparatively smaller egg and yolk sac, as well as for shrimp. Historically, attempts to replace live feeds wholesale with manufactured feeds have resulted in unacceptably high mortality and low growth, although research is advancing steadily in this area. Therefore, larvae are often started on mixes of microalgae with rotifers (a zooplankton, or microscopic member of the animal kingdom). They will graduate through appropriate sizes of rotifers until they are able to consume Artemia, before moving on to manufactured feeds at the appropriate stage of development.

Artemia characteristics and biosecurity considerations

Artemia, also called brine shrimp, are crustaceans. They are often used in an immature form themselves (decapsulated cysts, hatched nauplii, juveniles, etc.) as an aquaculture feed. Their most important characteristic is that, in their metabolically-inactive cyst state, Artemia are extremely resistant and can thus be dried, canned, shipped and stored, remaining on-hand until they are needed as feed, when they are incubated in seawater until hatching. This makes Artemia cost-efficient and convenient compared to other live feeds such as rotifers (which often have to be grown by the hatchery itself at considerable effort), helping it to secure an important position in the diets of practically all commercially produced shrimp larvae as well as the larvae of a significant number of marine finfish.

Artemia cysts may be graded on a number of characteristics. One is size; smaller Artemia can be fed successfully to species whose larvae are tiniest, and thus most vulnerable. Another is fatty acid content, although technology exists to “enrich” Artemia with nutrients including EPA in order to boost survival and growth among the larvae which go on to consume it. Finally, Artemia cysts are also graded on synchrony of hatching. As explained by Dr. Patrick Sorgeloos, professor at the University of Ghent and a leading expert in Artemia, this is important because brine shrimp which have entered stage 2 of their development begin feeding themselves from the microbial environment of the water, an environment which in many cases includes Vibrio. This means that even if you disinfect the outsides and water of the Artemia after that point, you won’t get the Vibrio they have ingested, he explains. Therefore, it is critical to many applications to have Artemia which hatches at the same time and to feed them to the larvae shortly after hatching to avoid the biological risks posed by these overly-mature individuals.

Artemia cysts may be graded on a number of characteristics. One is size; smaller Artemia can be fed successfully to species whose larvae are tiniest, and thus most vulnerable. Another is fatty acid content, although technology exists to “enrich” Artemia with nutrients including EPA in order to boost survival and growth among the larvae which go on to consume it. Finally, Artemia cysts are also graded on synchrony of hatching. As explained by Dr. Patrick Sorgeloos, professor at the University of Ghent and a leading expert in Artemia, this is important because brine shrimp which have entered stage 2 of their development begin feeding themselves from the microbial environment of the water, an environment which in many cases includes Vibrio. This means that even if you disinfect the outsides and water of the Artemia after that point, you won’t get the Vibrio they have ingested, he explains. Therefore, it is critical to many applications to have Artemia which hatches at the same time and to feed them to the larvae shortly after hatching to avoid the biological risks posed by these overly-mature individuals.

Indeed, pathogen control, and particularly Vibrio control, is of utmost concern when using Artemia. Unlike rotifers, which are farmed on algae, often in-house, nearly all commercially-relevant volumes of Artemia are from wild harvest. Dr. Sorgeloos estimates a mere 40 tons or so out of a total harvest which is believed to amount to at least 3,000 tons comes from “farmed” Artemia, mainly as part of poverty reduction programs in southeast Asia, and while he observes the quality to be extremely high, it is understood that the price point makes them currently uncompetitive for all but the most specialized of applications. Therefore, a major preoccupation in the Artemia industry is ensuring that the use of wild-bred organisms does not introduce disease in the sensitive hatchery environment. For his part, Dr. Sorgeloos is adamant that with careful and correct attention to biosecurity protocols—by the users as well as by the suppliers of the Artemia—this organism can be used without excessive risk to the hatchery. But it is worth acknowledging that many others view Artemia as not necessarily the cleanest of feeds and view biosecurity as an important reason to move away from Artemia as much as possible.

Artemia origins and availability

The other major reason the industry has long been interested in diversifying away from Artemia is because of perceptions that the supply is vulnerable to disruption. In the words of Dr. Schwarz, “we really can’t increase Artemia production. It’s a wild harvest, it’s a relatively finite feed source, and you will see cycles globally in prices of Artemia based upon wild harvests; when there’s really good years and there’s more Artemia, the price goes down, and when there’s bad years on the harvests, there’s less Artemia and the price goes up.”

The natural habitat of Artemia is inland salt lakes. Throughout much of the period since aquaculture began using Artemia in feed, the Great Salt Lake (GSL) in the US state of Utah has been the most important source of wild product. However, this dependence on the GSL has traditionally left the market at the mercy of environmental conditions which upset the yields of the lake, a situation which can cause dramatic fluctuations in the price. Famously, the GSL Artemia harvest dropped from about 15 million pounds gross weight to about 6.1 million pounds gross weight in the 1997-1998 harvest because of a decline in salinity, according to the USGS.

Although sources have diversified somewhat in recent years, spreading into the former Soviet republics of Central Asia and to parts of China, the GSL is still believed to provide between a third and a half of the world supply. As admitted by Dr. Sorgeloos, definitive numbers around production in these areas are unavailable and harvests naturally fluctuate, so it is not possible to be sure of the market share of any particular source. However, as a rule, inland salt lakes throughout the world are under intense ecological pressure as water sources are diverted for other industrial or agricultural uses, and there are questions about whether the supply will be able to keep up with the projected growth for the aqua hatchery industry.

What’s next for hatchery diets?

It is therefore unsurprising that researchers have dedicated much attention to the search for suitable alternative feeds for hatcheries. “I’ve been in aquaculture for over 30 years; even in the private sector, and even back then, we were constantly involved in in-house R&D looking at Artemia replacements,” says Dr. Schwarz.

Some are looking at deploying live feeds differently. For example, the use of rotifers could be prolonged until the animals are ready to be fed on microdiets; “for quite a few species, we have gone from rotifers, completely skipped over Artemia, and gone straight to microdiets which are commercially manufactured,” observes Dr. Schwarz. “There’s several species now where that’s become the commercial protocol…red drum, for example.”

Another alternative are copepods, tiny crustaceans which form the link in the food chain between algae and larval fish in the wild. This makes them attractive as a food source in the hatchery as they are nutritionally well-adapted (compared to Artemia, which are not naturally part of the ecosystems where these fish evolved and which in many cases must be “enriched” in supplemented water to be nutritionally well-adapted as a feed for larvae). Indeed, as explained by Dr. Schwarz, some larvae seem to do so well on copepods that they have accelerated development of the digestive system, allowing an earlier transition to manufactured diets. However, it is understood that copepods are currently much more expensive even than rotifers to culture, although the segment is evolving rapidly.

Others are looking into taking the drastic step of eliminating live feeds entirely; after all, growing one’s own rotifers and other plankton is a complicated, resource-intensive operation that many hatcheries would be happy to be rid of. However, this remains some ways off: “I don’t see that happening today or tomorrow,” says Dr. Schwarz. Although it is understood that there has been some success in bringing several species to maturity without live feed, mortality with 100% microdiets is still rather higher than would be the case with live feed, and further development is necessary before this will be a commercially-feasible proposition. “If we look very far into the future, I can envision in a lot of the commercially-produced species a complete elimination of live feeds, and there’s going to be [other] species where we just can’t because of biological limits,” acknowledges Dr. Schwarz.

Meanwhile, co-feeding using a small amount of live feeds augmented with manufactured feeds could potentially be quite successful as a strategy to minimize a hatchery’s exposure to the risks of live feeds, while still keeping their presence for benefits such as stimulating the development of the digestive enzymes in larval fish. Indeed, the work of the last few years has been transformative in reducing our use of Artemia while not eliminating it entirely. “20 years ago, one needed about 15 kilos of Artemia to produce 1 million shrimp post-larvae, today one can do it with 3-4 kilos. That’s because there are more performing artificial diets,” asserts Dr. Sorgeloos. According to him, both the geographic diversification of Artemia supply and the industry’s hard work to use it more efficiently have been instrumental in stabilizing the price and ensuring that the resource will stretch as far as possible.

It would therefore be a mistake to think that aquaculture is ready—or even necessarily looking—to take Artemia out of the hatchery for good. “It’s not that there will be less Artemia; Artemia will probably remain about the same, supply-wise, but the demand for live feeds will go up, so it will take a smaller market share as the market grows,” says Dr. Schwarz. “I don’t see a big problem coming, it’s just a natural shift.” Do we need to use wild Artemia more efficiently? Yes, certainly. Do we want to diversify in order to allow the industry to grow? Yes, certainly. But nobody’s saying Artemia cannot or should not be used in aqua feed, and it seems a safe bet that it will continue to play a central role in the hatchery. As Dr. Sorgeloos observes: “Already in 1975, when I finished my Ph.D. and was giving a presentation in France, people said ‘how can you be so crazy as to work on Artemia…because in the very near future we will not need Artemia anymore.’ I have heard that many times in the past 30-40 years, and we are not there yet.”