Apocyclops panamensis - DEVELOPING A PROMISING COPEPOD FOR AQUACULTURE  

Copepods are often considered to be nearly ideal live feeds for many larval fishes because they can provide nutrition superior to rotifers, and the early-stage nauplii of some species are smaller than even the smallest rotifer strains currently in use. Nevertheless, the use of copepods in larviculture has been limited because they are significantly more difficult to culture than rotifers. Common difficulties include limited culture densities, requirements for live algae as feed, and failure of cultures when they are invaded by ciliate protozoans.

The cyclopoid genus Apocyclops has not received as much attention from aquaculturists as other copepods such as Acartia and Parvocalanus. But Apocyclops includes several species (e.g., A. borneoensis, A. dengizicus, A. distans, A. panamensis, and A. royi) that have been cultured. In general, all these Apocyclops spp. were capable of rapid growth and development, often demonstrated over a range of salinities. They are rather omnivorous, capable of feeding on a variety of different microalgae and even yeast (A. dengizicus), but performing much better on higher-quality microalgae that are good sources of HUFAs, such as Isochrysis and Tetraselmis.

The best-studied species are A. dengizicus and A. royi.  A. dengizicus has N1 nauplii 75 µm wide and 120 µm long, tolerates a wide salinity range, and develops from egg to adult in only 7.4 days at 35 °C, with a population doubling time as short as 2.2 days. Fecundity can be as great as 647 nauplii/female. A. royi is widely used for aquaculture in Taiwan. Its N1 nauplii are 110 µm long, it is also euryhaline, and different isolates may have different temperature optima. It is especially noteworthy that A. royi has been shown to prey upon and effectively suppress two troublesome invaders of copepod cultures, Brachionus rotifers and the ciliate Euplotes.

Although Apocyclops panamensis has been shown in pond culture to be good first feed for Red Snapper, there is little published information its basic biology, such as optimal salinity, temperature, feeds, growth rates, reproductive capacity, and other life-cycle parameters. At Reed Mariculture we have very encouraging results with production trials. A. panamensis has small N1 nauplii measuring 70 x 100 µm, and it is very hardy, tolerating a wide range of salinity and  temperature. It thrives on commercial algae concentrates, so no live algae are needed, and ciliates are never detectable in cultures. We are now further developing the potential of A. panamensis by selective breeding with the goal of reducing the size of N1 nauplii and increasing its tolerance of high culture densities. The efficacy of selective breeding has been shown in other copepods, in which as few as 5 generations of selective breeding can yield significant changes in body size, fecundity, and resistance to algal toxins. Domestication of rotifer strains and use of concentrated feeds has made it possible to increase culture densities over 1000-fold. The future of aquaculture will depend on such development of domesticated strains of aquatic species  that can thrive on commercially-available feeds in intensive culture systems.