REARING OF LARVAL FISH IN COCULTURE WITH COPEPODS

Better aquarium technologies and more hobbyists have led to a higher demand for marine ornamentals.  However, only a few species have been successfully reared in captivity , leading to increased pressure on coral reefs to meet the demand for ornamental fishes and invertebrates.  In their native habitat, many larval fishes depend on copepods and other zooplankton as their primary food source. The challenge has been  to develop culture  technologies  that  produce  enough copepods to sustain and meet the larval fish's dietary needs, especially at the commercial level.  We have been using the clownfish (Amphiprion ocellaris)  as a model to develop a protocol for raising the larvae in coculture with copepods (Parvocalanus crassirostris) .   The goal is to reduce the number of copepods needed from stock cultures by creating a self-sustaining  copepod population in the rearing tanks, which serve as a continuous food source for the larvae.

In feeding studies, we found that young fish  feed voraciously on the immature stages of the copepod but cannot capture the adult s.  Thus, fish larvae eat early nauplii and copepodites, while adult copepods reproduce . In our coculture larval rearing strategy, we establish a healthy copepod culture in the rearing tank one to two days before the fish eggs hatch.

In a pilot study, we started with 10 1-day-old clownfish larvae.  At 14 days post hatch (dph), the remaining  eight clownfish had dev eloped their characteristic coloration and settled .  Copepod abundances in the rearing tank remained high until 10 days post hatch (dph) .   At this time,  the larvae were able to capture adult copepods and they decimated the copepod population.  Fish we re transitioned to Artemia nauplii and flake food reducing the need for copepods.

Feeding investment in terms of number of copepods was much lower than under the traditional daily feeding regime.  A total of 13,800 copepods were invested from the stock cultures on three days (days: -1, 1 and 10; Fig. 1) .  In contrast, if larvae had been raised by daily addition of copepods, approximately 121,000 copepods would have been needed. After settling, l arvae reared in coculture continued  thrive reaching two centimeters at 35 dph (Fig. 2).