Killer aquariums: One Texas-based scientist's effort to breed tropical fish andsave dying coral reefs
to spawn or not to spawn?
After a diving trip in the Caribbean 20 years ago, Joan Holt became interested in raising tropical fish in her lab — especially after learning that nearly 100 percent of the colorful fish in our aquariums are collected from the wild and that a huge majority of them die from the process.
Holt has spent the larger portion of her career at the University of Texas Marine Science Institute in Port Aransas studying the rearing of commercial fish species (like red drum), and her work has been put to practical use in state and commercial hatcheries and aquaculture operations.
Stocking aquariums is a $1 billion industry, moving an estimated 30 million reef fish around the world each year, but removing that many fish from the ocean can have a negative effect on the health of reef environments. Certain species of fish, for example, eat algae and, if their numbers become too low, overgrowth of algae can suffocate corals.
The methods used to collect these fish can be harmful as well: Cyanide, used as an anesthesia to make fish easier to catch, can bleach the coral and kill or harm other species, especially those that can’t swim away. Cyanide is also one reason almost 80 percent of collected fish die soon after capture. Many of the rest die within a year in captivity, despite the fact that many species live for decades on the reef. In addition to cyanide, fish sometimes die from being brought up from depth too quickly, loss of protective scale coating due to handling, poor water quality and being deprived of food for days during transport.
Holt hoped she could help solve these problems by figuring out how to raise tropical fish in captivity.
It proved a huge challenge. First, she had to figure out a harmless way to collect a small amount of tropical fish to begin her research. Trial and error led to a rather low-tech method: two divers (one with a hand net or large plastic bag) and another to carefully herd fish toward the bag. Next, she had to convince those wild fish to reproduce in the lab. Based on efforts with commercial species, Holt knew fish will spawn if lab conditions match those in the natural world, so she studied temperature and day length at locations such as the Florida Keys and Jamaica and replicated those conditions for her studies. Eventually, she successfully spawned 18 ornamental species.
The next step, growing baby fish (larvae) into adults, had been tricky enough with commercial species, and it turned out to be even more challenging with tropical ones. Some tropical species spawn in the open ocean, and their larvae hatch in a relatively undeveloped state, not yet able to eat on their own; others attach eggs to a solid surface, one or both parents care for them (think of Nemo’s dad, Marlin), and larvae hatch ready to start eating. The former were much easier to raise in the lab, but Holt focused on the more complex ocean-spawners — i.e., the most popular kind of aquarium fish.
In general, tropical fish larvae put picky eaters of any species to shame, so figuring out what to feed them was no easy task and the mystery remains somewhat unsolved. Work on refining the fishes' preferred menu continues at the MSI, with the ultimate goal to identify food that can be grown in the lab or easily collected.
Meanwhile, another major challenge in breeding tropical fish was creating the right water conditions for the captive fish and figuring out how to feed them, without turning the water into a terrible mess. The lab eventually hit upon a tank design that accomplished both. Ultimately, Holt was able to get seven of her original 18 spawned species to grow into adult fish that produced their own offspring: lined and pygmy seahorses, comet fish, jack knife fish, cubbyu, and fire and peppermint shrimp. These species can conceivably now be commercially produced.
Aside from producing these fish in commercially viable numbers, the next step, in Holt’s mind, is developing some way to tell buyers what they’re getting: fish raised sustainably in a lab or fish collected from the wild with potentially harmful practices. To help distinguish the eco-friendly method from the rest, she envisions a certification process, or paper trail, similar to that used in organic farming.
Many hobbyists, she believes, would support sustainable captive breeding — at least in part because those captive-bred specimens will likely have better survival rates than wild-caught ones, many of which survive only a few days or weeks in home aquariums.
Holt is working with other scientists on a marine ornamental aquaculture book. She hopes more people will come to see captive-raised ornamentals as an important conservation tool that helps protect tropical reefs and their occupants in the wild.
So, what will you keep in your aquarium?