COPEPOD NAUPLII AS FOOD FOR MARINE ORNAMENTAL FISH LARVAE
The harpacticoid copepod Euterpina acutifrons was isolated from local waters more than 15 years ago by Syd Kraul, then of the Waikiki Aquarium. The Aquarium has since been the state's major source of the culture, and has helped many individuals and organizations by providing starter material. However, the species is neither endemic to Hawai'i nor uniquely cultured here. It is a circumtropical species that has been mentioned in culture research literature for decades.
E. acutifrons has some technical advantages over other commonly used food items, and now that methods have been developed, it appears that production need not be more expensive than growing other feeds. The advantages are: 1) the early stages are smaller than most cultured feeds and freshly hatched brine shrimp; 2) they are more nutritionally dense (less watery, with more organic matter and calories per unit of fresh weight) than rotifers, similar to brine shrimp; 3) when grown under good conditions, they are at least as good as any other item in content of essential amino acids and fatty acids before enrichment; and 4) they move with the characteristic jerky motion of copepods and thus are more likely to be recognized as food by larvae. Mahimahi, groupers, and other fishes generally take E. acutifrons enthusiastically. The size and motion advantages are the most important. Alternative small items (e.g. oyster larvae and artificial particles) are expensive, and though they can be of good composition, may not attract the larvae.
E. acutifrons has been used in "extensive" larval rearing trials, in which fish eggs or larvae were placed into large outdoor tanks with microalgae and a starter culture of copepods. The fish were then allowed to (hatch and) forage for themselves, while the green cells and copepods provided a food chain to support them for a time. This strategy can be inexpensively begun, and though nog efficient in terms of water volume, there is little cost of human labor. Encouraging results have been observed with mahimahi and groupers.
Copepods hatch as "nauplius" larvae (plural: nauplii), simple ovoid bodies with just a few appendages. They add segments and appendages as they molt and grow. E. acutifrons' first nauplii have their smallest dimension at about 40-50 microns, rather smaller than small rotifers; the adults, even with attached egg masses, are less than 1 mm long and about half the weight of brine shrimp nauplii. Cultures usually contain all stages, but animals of a desired size can be harvested with screens.
Alternatively, one can screen out adults to start a culture that will produce a well-timed batch of nauplii. The generation time of this fast-growing animal is a week or less at the optimal temperature of 26 C. At the Waikiki Aquarium, they are cultured in 450 l square tanks, stirred and aerated with large (not air stone) bubbles, and fed the cultured microalgae Chaetoceros, Tetraselmis, and sometimes Nannochloropsis. Chaetoceros alone can do well, as may the others used singly. It is possible that E. acutifrons could be grown on cheaply-obtained particles and later enriched. Several of our creative growers of freshwater ornamentals produce live feeds on a mixture of yeast and blender-ground flake feed.
Other copepod species have begun to attract research attention for use with marine ornamentals, as reported by researchers from the University of Texas and Florida State University at the recent Marine Ornamentals '99 conference on the Big Island. At this meeting the Aquarium reported on early feeding of masked angel fish on E. acutifrons. The copepod is also used to feed larval invertebrates, as well as later stages of seahorses, pipefish, black coral, wire coral, cup coral, anemones, mandarin fish, sea jellies, mysid shrimp, and wild caught plankton. This species stands as a ready resource for development of marine ornamental culture.
(excerpts from article by J.P. Szyper, K. Brittain, C. Tamaru, H. Ako
in Makai Sea Grant College Program, Vol. 22, No. 1, January 2000)