What are the guidelines for culturing brine shrimp?
The benefits of feeding live artemia are well known and accepted in the aquarium community. Alternatively, there are many convenient and well-formulated artificial, inert diets that purport to completely eliminate the need for such live food. These prepared diets and, more importantly, the specific amino acids, lipids, and vitamins they contain are, if not complete replacements for live feed, often necessary additions to a single species diet lacking in one or more of the essential nutrients.
That having been said, seldom does a soggy, inanimate particle of gelatinized starch and dried fishmeal ignite the feeding response in fish like the herky-jerky swimming antics of a live brine shrimp. For this reason, live brine shrimp will always be an integral part of the solution for sustaining healthy aquarium populations.
In addition to moving about the water column, live brine shrimp have a number of other useful traits, namely:
- They are soft and easily digestible and contain enzymes that help fish to better utilize other feeds;
- They are high in protein, ranging from 55% to 60% protein by dry weight, supporting rapid weight gain in young fish;
- They can be enriched with other feeds or additives, a process often referred to as "bio-encapsulation" in order to deliver HUFAs, antibiotics, or other nutrients to the target species (see SELCO);
- They can be fed to both marine and freshwater fish, surviving and swimming for hours — even in fresh water;
- They originate in hyper-saline biotopes and, therefore, they are seldom vectors for diseases that affect fish;
- They grow quickly, multiplying in weight 500-fold in three to four weeks and increasing in size from 450 microns to 1.5 centimeters in length.
Yet, raising brine shrimp to maturity in useful numbers is not an easy task; and you can expect to spend as much time at it, if not more, as you would breeding and caring for baby fish — often with less-than-hoped for results. The following primer is designed to help obviate the need to commit the most frequent mistakes — most often, the mistakes of overstocking, overfeeding, underfeeding, inadequate aeration, under-filtration, and providing inappropriate feeds.
Given the myriad ways to inadvertently kill these critters, even in a comfortable, controlled environment, it seems counter-intuitive, if not downright discouraging to the aquarist, that an animal of prehistoric pedigree can, in its natural setting, be left high and dry in the summer, desiccated for months under the hot sun, forcibly removed to a faraway clime in the gut of an avian migrant, re-deposited in a hyper-saline lake devoid of life, and subjected to subfreezing temperatures, only to emerge from its capsule to thrive again and even propagate.
Without further rumination, let's assume that we've successfully hatched the eggs and wish to culture the brine shrimp. Can we not, as our well-intentioned Webmaster asked, just send them off to a French finishing school?
Culture Tank
The culture tank can be as simple as a 5-gallon bucket or as involved as a $500 Kreisel tank. The important design considerations, when choosing or building a culture tank, are to allow for temperature control; adequate aeration (to maintain dissolved oxygen levels as well as to suspend food particles); internal or external water filtration and/or partial water replacement; and the concentration and evacuation of detritus, mortalities, and fecal matter (through screened drainpipes or siphoning). Culture systems are varied, from batch or static systems, to sophisticated flow-through tanks for high-density culture. If the intent is simply to observe a small number of brine shrimp, an aquarium with a sub-sand/mud filter and one or two directional airlift standpipes is ideal.
Stocking
To improve your chances of success, start with stocking densities of 1,000 animals per liter or less.
How does one count 1,000 miniscule baby brine shrimp? The easiest way to manage artemia counts is to sample from a randomly distributed population by extracting small aliquots of the whole, counting, and then extrapolating. Let's assume that we began with one gram (about 1/2 teaspoon) of an 80% hatch-out quality egg. If, after 24 hours' incubation, we recover most of the newly hatched baby brine shrimp, we would have upwards of 200,000 baby brine shrimp!
To test our theory of aliquot sampling, transfer all the animals into a one-liter bottle containing clean seawater with aeration. The aeration will keep the brine shrimp in suspension, and thus randomly distributed throughout the cone or bottle. Using a one-milliliter pipette, extract one milliliter of water, and with it, approximately 1/1000th of the total population (1 liter = 1,000 milliliters). If our sampling technique is adequate (replicates are advisable), we should have about 200 animals in our aliquot sample. If a pipette is not available, a calibrated eyedropper can be used to pull a measured sample from the bottle.
Note: If this process has already exceeded your tolerance for tedium, you may want to consider stopping here, enriching all the newly harvested brine shrimp contained in the one-liter bottle with SELCO, and feeding the fortified baby brine shrimp to your fish or seahorses. But, if you insist on bigger and beefier brine shrimp, then read on. Just remember — you had your chance!
Water
The preferred salinity range for culturing brine shrimp is 35-40 ppt (specific gravity 1.024-1.028). Unlike in the preparation of hatching solutions, where household brands of baking salt, kosher salt, and solar salt are adequate, culture water should be pre-mixed using an aquarium-grade marine salt. Remember to pre-mix and stock additional water for use later. You'll need it!
The initial pH should be between 7.5 and 8. The pH is likely to fall during the culture period and can be adjusted upward with the addition of baking soda or NaHCO3. Monitor pH regularly and adjust as needed.
Artemia are generally tolerant of low dissolved oxygen levels. Oxygen stress is often indicated by a reddening of the animals caused by the increased presence of hæmoglobin. Providing adequate aeration to keep food in suspension usually eliminates any DO (dissolved oxygen) concerns. Keep in mind that small bubbles are more efficient vehicles for oxygen transfer, but that very fine bubbles actually foul the swimming appendages and interfere with feeding. If the DO level falls below 2.5 mg/l-1, add additional airstones.1
Temperature should be maintained at between 20° Celsius and 25° Celsius (68°F-79°F). Remember that replacement water should be of similar temperature to avoid thermal shock.
Feeding
Artemia are continuous, non-selective filter feeders.2 The most difficult challenge in culturing artemia is providing appropriately sized feed in sufficient concentrations without unduly compromising water quality. Fortunately, there are a number of easily obtained feeds that are optimal in terms of both size (less than 20 microns) and nutritional content.
Tank design and aeration play an important role in the distribution of feed throughout the water column. Feed must be kept in suspension in order to be utilized. This is accomplished by the use of directional airlifts, air stones, and return water flows. When using dry feeds, better food suspension is achieved by premixing the feed with clean seawater.
Nitrogen levels should be monitored. NO2-N levels should be kept below 320 mg/l-1.3 Water quality is controlled by a combination of mechanical filtration, either external or internal, and or dilution with new, clean water.
In order to maintain adequate water quality, the suspended solids, uneaten food, fecal matter, and detritus must be removed regularly. This presents the conundrum: How does one efficiently remove these pollutants without also removing the food? Unfortunately, there is not an easy answer. The approaches described in literature are more art than science, or glossed over altogether. Certain losses in food density due to filtration are unavoidable. Compromises often entail filtering out large flocks only (allowing food and suspended solids to pass through), allowing flocks to settle or concentrate near effluent drains before removing, using longer water retention times, and/or alternating between intermittent filtering and feeding cycles.
As animals grow, filters with larger mesh sizes can be used. A typical filter at the outset will have openings of 100 microns. These openings can be increased to 350 microns when the animals are about two weeks old. Filters must be cleaned regularly. Placing air stones in front of effluent filters will help prevent blinding of the filter. Obviously, increasing rates of water exchange and increasing filter opening sizes will necessitate a commensurate increase in feeding rates in order to maintain desired food cell densities.
Culture density, food cell density, and animal health can be checked by routinely removing and examining a beaker of water and holding it against a light for close inspection. It is possible to note the fullness of the gut and determine if the animals are adequately fed. Food cell density can also be measured by inserting a Secchi disc into the tank water to measure clarity. The depth that the Secchi disc is lowered into the water before it is obscured is observed and recorded. Feeding rates and exchange rates are maintained at a level that works for your particular system.
The preferred feed for artemia is cultured, live diatoms. A number of species have been used successfully, including Nannochloropsis sp., Tetraselmis sp., and Dunaliella sp. Providing live diatoms, of course, entails a duplicate effort commensurate with the number of artemia to be fed. As stated before, brine shrimp are continuous feeders and, at high densities, quickly clear water of diatoms. Reliance on live diatom cultures, though practicable, should be done so with substitute frozen or dry feeds within easy reach should your algae cultures crash.
One of the best choices in readily available feeds that we have found for culturing artemia are the cryo-preserved algae pastes, particularly Nannochloropsis sp. or the proprietary mix, Tahitian Blend, which contains several alga species and stabilized vitamin C. These pastes are non-viable, highly concentrated algal cells that can be administered to the culture tank drop-wise. Using cryo-pastes of known cell density can allow the culturist to quickly harmonize feeding levels with the density and growth of the artemia population.
Other feeds that have been used successfully to culture artemia are the spray-dried, single-celled yeasts, most notably Torula. Other feeds that have been used to culture brine shrimp are micronized forms of rice bran, corn bran, and soybean.4 These feeds are often used in combination with other approaches. The proper sizing of particles can be attained by micronizing (using an electric blender) brans with seawater and filtering through a 250-mesh or finer bag. Spray-dried Arthrospira platensis (formerly Spirulina platensis) has also been used to sustain brine shrimp. Feeds that readily leach nutrients into the water should be avoided, as they will contribute to high bacterial loads, increased oxygen demand, and fouling of swimming appendages.
General
As stated before, there are many and varied systems that have been devised for the on-growing of brine shrimp. For high-density culture (10,000+ animals per liter), survival requires robust mechanical filtration and water exchange — in effect, a raceway system with ancillary treatment and filtration equipment. Lower density (1,000 animals/lt.) "batch" systems rely on a combination of regular water exchange or dilution with clean seawater and regular removal of detritus. In the batch system, feeding rates are lowered to compensate for longer water retention times, oftentimes resulting in slower growth. In either system, water quality is enhanced by the addition of a protein skimmer.
Disease
It is not uncommon for filamentous Leucothrix bacteria to emerge in the protein-rich culture environment. Vibrio sp. bacteria and other infectious diseases may present. These outbreaks may be treated with antibiotics and/or controlled by increasing salinity. It is important to use disinfected cysts and to routinely disinfect culture apparatus with a hypochlorite solution.
As suggested earlier, producing live adult artemia in sufficient numbers to feed numerous fish tanks or seahorse pens requires considerable work. The demands of feeding artemia and cleaning filters are non-relenting 24/7. On the other hand, low-density culture of artemia is rewarding and less trying. Our best advice is to start small and scale up gradually.
References
1Manual on the production and use of live food for aquaculture. FAO Fisheries Technical Paper 361, Lavens, P and Sorgeloos, P. 1996, p. 168.
2Ibid., p. 175.
3Ibid., p. 171.
4Ibid., p. 174.