It has been well over a decade since Yellow Tang breeding research began at the Oceanic Institute in Hawaii (OI), with many folks along the way making progress on tang breeding in general. When it comes to Yellow Tangs, the most notable progress to date had occurred at the hands of Syd Kraul in the early 2000’s, and while rumor upon rumor have piled up over the years, until this week no one had really proven they could go past Kraul’s 40 days post hatch with Zebrasoma flavescens at Pacific Planktonics back in 2004/2005. Even Kraul, who thought he’d have closed the gap by 2007, never seemed to get any farther.
That has changed today with word from Chad Callan at OI, who announced on Monday via the Rising Tide Conservation Blog that they have passed the 50 day post-hatch milestone with captive spawned Yellow Tangs. As he wrote, “On Jan 1, 2014 we stocked a 1000L tank with about 40,000 yellow tang eggs. In this rearing attempt we experimented with very high water turn-over rates, and very clean (ultra UV dose) water. As in previous studies, we used the calanoid copepod,Parvocalanus crassirostris, as our feed. While this was only one tank (we are currently testing these methods again), we immediately noticed far more fish making it through the early larval period than ever before. We were really excited to see 1000’s of fish survive past the first 2-3 weeks and ended up with more than 600 at day 35. We have since moved the fish to smaller tanks and are investigating potential settlement cues, like photoperiod and substrate.
The fish recently crossed day 50 and appear to be looking very close to settlement. We’re observing fairly high mortality during this period of transition, but still have more than 150 fish distributed among our tanks. We are hoping at least a few make it through, but regardless are very encouraged by this recent progress!”
I asked Chad to provide some insights and explanations, most notably his mention of “ultra UV dosed” water. Callan elaborated that the used a “High-output, 300W UV that we only ran 5liters/min through. If you do the math, based on the manufacturer specs, that’s >4,000mJcm2. The combo of high UV dose and high turnover rate are what (we think) helped provide a more hospitable environment( bacteria-wise) for the fish.” Indeed, as breeding enthusiasts will continue to learn in the weeks and months ahead, there is growing evidence that bacterial populations (and similar) are seeming to have more and more of a negative impact on rearing when it comes to pelagic spawning marine fish. It seems ever more likely that “sterile” tendencies might be a very necessary (and frustratingly difficult to provide) component of marine fish breeding.
Some other interesting tidbits; natural saltwater from a well is being used for these initial rearing efforts. Is there something beneficial at play here that artificial saltwater can’t match? Impossible to say at the moment, but it’s a question that has come up more than once now in relation to fish breeding. Callan mentioned that rearing vessels themselves were nothing unusual either. Their largest obstacle so far has been the production of sufficient populations of Parvocalanus copepod nauplii, which are THE only food they’ve used until the larval Zebrasoma start taking brine shrimp nauplii.
Settlement is believed to be around the corner; send the well wishes and good vibes to the team in Hawaii as their fish approach metamorphosis, a time typically frought with difficulty and more mortality (They’re down from 40,000 eggs to around 150 larvae at this point in time!).
For the full story, visit the Rising Tide Conservation Blog.