Reef Ramblings

The third in the series of articles on breeding marine fishes continues on the subject of larval nutrition. This article looks at Artemia, describing what they are, their role in larviculture, and presents a basic protocol to allow you to culture them yourself.

What are Artemia?

Artemia, otherwise known as brine shrimp, are small filter feeding crustaceans starting at about 450 microns long for newly hatched nauplii and up to 20 mm long for adults, newly hatched nauplii and adults (if suitably enriched) can offer good nutrition for both corals and fish.

This is probably the most widely used of the live foods I’ve discussed in this series of articles, yet it’s also probably one of the most misunderstood. It’s a boon to aquaculture and to anyone wanting to breed and raise fishes, yet at the same time it can be the cause of disease and malnourishment.

Artemia salina is something of a curiosity. It’s not actually a marine animal, it’s found in salt lakes and brine ponds all around the world, usually in extreme biotopes. These are bodies of water where the salinity can be more than 300 ppt, with the consequence that only a few species of bacteria and algae can survive. As one of the few invertebrates capable of adapting to these extreme conditions Artemia can take advantage of the lack of predators and food competitors, and develop into very dense populations. Part of the adaptation to extreme habitats is Artemia’s mode of reproduction, the very thing that makes them so useful to us. Many of the salt lakes or brine ponds inhabited by Artemia will, from time to time, dry out. As the salinity increases, instead of the cysts hatching out they develop a thicker outer shell and, when released, float. These are dormant cysts that can become blown ashore or remain in a dried up pond and then, when rehydrated at a later date, hatch out. This is a superb adaptation to the sort of extreme environment that they inhabit, salt pools that go through a cycle of drought followed by seasonal rainfall. It preserves the existence of the species and, very usefully for aquarists, it gives us a convenient live food that can be available at 24 hours notice any time of the year.

Artemia is widely available in aquatic shops as Artemia cysts or eggs. Artemia cysts are big business owing to their importance to aquaculture. Accordingly they are graded by size, percentage hatch out, and nutritional profile to cover the requirements of the different species being raised. On the larger packages of Artemia used in aquaculture you’ll see figures such as: 90% Hatch Out, 250,000 Nauplii per gram, Nauplii Size <450 microns. There may also be figures for hatch out time; this is based on a certain percentage, e.g. 90% at 20 hours. There are premiums for smaller nauplii size and for hatch rate with higher hatch out rates commanding higher prices.

Most suppliers grade their products as 90%, 80%, 70%, and so on. Grades below the 70% mark – 60% and 50%, are sold on at much lower prices. Care to guess where the majority of Artemia sold in the aquarium trade comes from?

Artemia cysts are available in either their natural form or as encapsulated cysts. Decapsulated cysts have had their shells removed, this is desirable for a couple of reasons: less energy is required for the nauplii to hatch resulting in a more nutritious product, higher hatch rates can be achieved, and there are no empty indigestible shells present. For most hobbyists I’d suggest sticking with decapsulated, it’s an easier product to deal with, no more faffing around separating live nauplii from shells, and in a reef tank it has the advantage that you can use unhatched cysts directly as food. Note: unhatched cysts contain higher levels of nutrition than newly hatched nauplii.

Culturing Artemia.

This is a very easy straightforward process. You can buy Artemia hatchers in a number of sizes, from 200ml upwards. Artemia hatchers are generally designed with a conical base where the air is introduced; this design in combination with good aeration ensures that the cysts are kept in suspension. You can also, of course, culture in our trusty 2 litre drinks bottle, you won’t get as high a hatch rate as with a properly designed culture vessel but they’re cheap and you can just junk them when they get dirty. If you take a look at some of the aquarium books on the market, or do a search on the web, you’ll quickly find lots of ways to make a DIY brine shrimp hatcher. For most hobby use it doesn’t matter too much what you use, but if you’re trying to raise larval animals I’d suggest using a couple of the inexpensive 200 ml hatchers in rotation, so that you always have freshly hatched Artemia available.

Once you’ve chosen your culture vessel, add saltwater of the desired salinity, as discussed in previous articles in this series. As with phytoplankton and rotifers, you’ll be relying on room temperature, so make sure your hatcher is within the range of 20˚- 30˚ C. Artemia aren’t fussy about temperature but do try to keep it stable. Aerate vigorously to keep the cysts in suspension without having them blown out of the water and sticking to the sides of the hatcher above the water line.

Hatching time will be dependent on temperature, grade and age of cyst and a couple of other factors. Cysts may hatch as early as 12 hours but I’d suggest harvesting after 24 hours. Unhatched cysts could be left for another 24 hours before final harvesting, or, if decapsulated, fed into the reef anyway.

To harvest, turn off the air and wait for any debris to settle; as the newly hatched nauplii are phototropic – attracted to light – you can use a light to concentrate them in one place, then siphon or otherwise extract them from the culture.

Note: If using natural cysts, the empty shells will float to the top, the unhatched cysts sink to the bottom, and the nauplii will congregate just above the bottom (unless attracted towards a light). Use a light to concentrate the nauplii as above.

Take care not to introduce discarded shells to small animals, as they can prove fatal if ingested.

Collect the nauplii together in a brine shrimp net or collector and thoroughly rinse with clean seawater before using. Never allow any of the culture water into the tanks you’re feeding.

If feeding newly hatched nauplii, make sure you use them within twelve hours of hatching, as up until that time they have a very good nutrient profile; after that time, unless they are enriched, they are nutritionally poor. At twelve hours a nauplii will go through its first moult and then start feeding. Newly hatched nauplii don’t have a mouth and go through fifteen moults, gaining appendages at each stage, before becoming an adult.

When growing Artemia on, it’s necessary to feed them and perform water changes to maintain water quality; all those moults need to be removed, otherwise over time detritus composed of moults and faecal matter will build up, providing a breeding ground for unwanted bacteria.

Artemia are filter feeders utilising just about anything smaller than around 50 microns, including phytoplankton, bacteria, yeast and a whole list of inert manmade foods. For cleanliness I’d suggest sticking with phytoplankton, preferably live, most of the other foods will result in a dirtier culture that will need cleaning more frequently.

The colour of Artemia can change in response to both it’s environment and to what it’s been feeding on. Green shows they’ve been feeding on phytoplankton while red or orange indicates they’ve been living under conditions of low oxygen levels and feeding on detritus or bacteria.

By the way, if you see Artemia in your rotifer culture (or vice versa) don’t worry about it, as Artemia aren’t capable of consuming something as large as a rotifer.

Adult Artemia.

It’s possible to grow out the Artemia you’ve been culturing to adult size. Under good conditions they should live for around four months with mature females producing five hundred free-swimming nauplii a week.

Note: This is a different form of reproduction to that responsible for the production of the cysts we hatch out, which are produced in response to salt lakes or brine ponds drying out.

If you buy live adult Artemia from shops there’re a couple of precautions you should take. The nutritional value of these brine shrimp is going to be poor as they’re unlikely to have fed for some time and you also run the risk of introducing disease. To get the best out of them discard the water they come in, rinse them in clean saltwater (not water from out of you reef) and then transfer them to an aerated container of fresh saltwater.

Once in a clean environment you can then enrich them using phytoplankton prior to feeding them to your reef.

Problems Posed by Artemia.

At the beginning of this article I mentioned that Artemia could be the cause of disease and malnourishment.

Taking malnourishment first: if adult Artemia are used as the mainstay of a fish’s diet, without first being enriched, or if nauplii aren’t fed after twelve hours, then they’ll be of very little nutritional value. Taken to extremes, this could quite easily compromise the health of any animal being fed this way.

Use of Artemia as a successor to rotifers when feeding larval fishes can present dangers since larvae, used to stuffing themselves with smaller prey, try to gorge on something a little bit larger. Whereas with rotifers you feed by density, say 15 per ml, with newly hatched Artemia you should change to shrimp per larva, say 25 per day. This should prevent deaths through overeating or choking.

The biggest problem posed by Artemia is that of introducing potentially pathogenic bacteria into the aquarium.

Note: I strongly believe this to be of utmost importance to those raising seahorses as, typically, they are the animals most likely to be fed consistently with live artemia and are also the animals most likely to succumb to bacterial infection.

Scrupulous attention to hygiene, sterilising all water, culture vessels, and equipment before starting any live cultures, will help to reduce the risks.

You’re looking a something around one billion bacteria per ml of culture water with 10% of these bacteria being Vibrio species, a number of which are reported to be pathogenic in fish (see table below).

Vibrio Bacteria Reported to be Pathogenic in Fish. (Harald Mulder)
Bacterium	Disease / Symptoms
Aeromonas hydrophila	Erythrodermatitis
Aeromonas salmonicida	Boils / Welts
Aeromonas salmonicida ssp. nova	Erythrodermatitis
Vibrio alginolyticus	Vibriosis
Vibrio anguillarum	Vibriosis
Vibrio damsellae	Vibriosis
Vibrio ordalli	Vibriosis
Vibrio salmonicida	Hitra disease / coldwater vibriosis
Vibrio vulnificus	Vibriosis

This is one of the reasons you should never add culture water to your aquarium, and why you should always thoroughly rinse live foods before use. This is an aspect of live food culture that’s well known in aquaculture but only recently being investigated in ornamental marines.

It’s quite possible that a number of fish losses on importation are due to pathogenic bacteria in the food chain. Further, these types of bacteria may also be responsible for losses of new introductions to the aquarium, and for losses of established fish on the introduction of new tank mates. One theory here is that fishes can acquire resistance to various strains of bacteria, but when a fish with no resistance is introduced it may succumb to these resident strains. Ref.: Harald Mulder. Coral magazine Volume 3, Number 4.

Air pumps and Live Food Production.

When using air pumps in conjunction with live food production it’s a good idea to emphasise certain safety precautions. These are precautions that should always be employed when using air pumps. but become even more important in food production. where instead of being run continuously, the pumps are switched off from time to time in order to examine the progress of a culture.

Always use a one-way valve between the culture and the air pump to prevent water back-syphoning occurring if the pump’s turned off. You can employ air valves to control the rate of aeration, but if you’re shutting the air off for any length of time it’s best to turn off the pump.

Positioning the air pump higher than the culture is also a good idea as it acts as a safety back up if the one-way valve isn’t working properly.

Make sure that the air pump you’re using has air filters, and regularly change them to help reduce airborne contamination.

Tim Hayes

Midland Reefs

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