ENVIRONMENTAL AQUARIST		BY JOHN TULLOCK

Captive Propagation

Marine aquarium dealers can only dream about a market the size of that enjoyed by their freshwater counterparts. Indeed, this is one reason why so few stores (although their numbers are increasing) are devoted only to serving the needs of marine aquarium hobbyists. In a typical aquarium shop (or the aquarium department of a full-line pet store) freshwater fish are relied upon to supply the “bread and butter” business, and saltwater specimens are a sideline. This situation will change in the future, however, as captive propagation of marine specimens becomes increasingly commonplace, and prices, especially for those species most suitable for the novice customer, come down as a result.

To see why the future of the marine aquarium industry depends upon the further development of the presently tiny marine aquaculture industry, one has only to examine the historical parallels to be found in the freshwater arena. A good example of the value of captive propagation is African cichlids. When first introduced into the hobby, these fish were scarce and expensive, due primarily to dependence upon collection of specimens from their native lakes in the Rift Valley of Tanzania. Transportation costs, deaths in transit and the unavoidable importation of parasites and pathogens along with wild fish dictated higher markups to compensate for significant losses of specimens — when compared, for example, to South American cichlids produced by Florida fish farmers. Today, many African cichlid species are hatchery-grown, prices have come down and these fish are among the most popular subjects for “advanced” freshwater hobbyists. That a similar scenario can result from an increasing supply of captive-propagated marine fish seems obvious.

Surprisingly, many aquarium hobbyists with whom I have spoken are unaware of the variety and quality of captive-propagated marine livestock that is now available. With the increasing popularity of reef tanks featuring many species of soft and stony corals and their relatives, invertebrate enthusiasts have a much wider selection of propagated specimens than do those who keep only fish. Nevertheless, the choices for fish-only fans are steadily increasing as more and more entrepreneurs see the potential for profit in this fledgling industry.

The common clownfish, Amphiprion ocellaris, was the first marine fish to be commercially produced. Today, most of the 30-odd species of Amphiprion, along with the maroon clownfish (Premnas biaculeatus), are available, although Premnas, together with A. ocellaris, Clark’s clownfish (A. clarkii) and the tomato clownfish (A. frenatus, probably constitute the majority of specimens sold owing to their popularity among hobbyists. The formerly rare and expensive “gold striped” color form of P. biaculeatus is now regularly available — and much cheaper- than its wild-caught counterparts were a few years ago.

Clownfish were a natural choice for the pioneers in commercial marine fish breeding, Martin Moe’s Aqualife Research Corporation and Aquarium Systems’ Instant Ocean Hatcheries, both of which were located in Florida. Both are now out of business, although not because they were unable to rear clownfish in large numbers. Not only are clownfish extremely popular with consumers, but their unusual reproductive physiology also lends itself to the needs of a would-be fish culturist. The gender of juvenile clowns is not resolved by their genetic makeup at hatching, but rather is controlled by the fish’s environment as it matures.

In nature, young clowns must locate and join an established family group that has already successfully occupied a host anemone. (While clownfish can be maintained successfully in the aquarium without an anemone host, in the wild these fish are never found away from the protection of an appropriate cnidarian after completing their larval development in the plankton layer.) A typical clownfish family grouping consists of a large female, a breeding male and several immature individuals. When the female dies, the breeding male changes sex and assumes the role of his former mate, and one of the immature fish becomes the breeding male. This pattern of development ensures that the anemone will be continuously occupied by a source of eggs for the next generation of the species.

The mechanism of sex reversal is incompletely understood, but the prevailing social milieu apparently plays a role. Females have functional ovaries with degenerate remnants of testicular tissue. Males have functional testes with undeveloped, but not degenerate, ovarian cells. Experimental removal or death of the female results in development of the dormant ovarian cells of the male, and degeneration of the testes. Apparently, when only juvenile fish are maintained together in the same aquarium, appropriate environmental cues are present to result in one individual’s development into a female and another’s development into a male, with the remaining fish, if any, “stuck” in the juvenile phase. Aquarium observations have led me to speculate that an individual’s aggressiveness may directly or indirectly influence this outcome. It seems plausible that a more aggressive fish might thus obtain the greater proportion of available food, would consequently attain a larger size and thus be better suited to the biological demands associated with egg production than its less feisty tankmates. Female clownfish are always larger than their male counterparts — in some species she may be more than twice his size.

Owing to the peculiarities of gender determination, obtaining a pair of clownfish is easy, as one needs only to place two juveniles (virtually all captive-bred clowns are sold as 1-inch long juveniles) in the same aquarium and then wait for them to mature. Clownfish could easily become the “guppy” of the marine trade as enthusiasm for spawning and rearing them at home becomes more widespread.

Clownfish are by no means the only species of marine fish currently available from hatcheries. C-Quest, located in Puerto Rico, is the largest commercial marine fish hatchery presently in operation, selling approximately 100,000 specimens per year. While clownfish form the bulk of C-Quest’s offerings, several other fish are routinely produced (see “C-Quest — The Leading Marine Aquarium Fish Hatchery for 1997,” by Joyce Wilkerson, Aquarium Frontiers, July 1997). Of these, the most popular among hobbyists are the dottybacks, all of which are members of the genus Pseudochromis.

The orchid dottyback (Pseudochromis fridmani) is endemic to the Red Sea, and is boldly colored in magenta. The sexes are indistinguishable in younger specimens, but as they mature, reaching about 2½ inches in length, males can be identified by the pointed extensions of the caudal fin. Many people who work with this species, including pioneer marine fish breeder Martin Moe, believe that a pair of this species can easily be obtained just by placing two juveniles together. When they mature, one becomes male and the other female. As with clownfish, species that can potentially be bred by the hobbyist enjoy a ready market, and the ease with which a pair can be established makes P. fridmani popular.

Several other Pseudochromis are available, though none is as spectacular as P. fridmani. These include the strawberry dottyback (P. porphyreus), the crowned dottyback (P. diadema) and the bicolor dottyback (P. pacagnellae) from the Indo-Pacific, along with three other Red Sea species, the striped dottyback (P. sankeyi), Springer’s dottyback (P. springeri) and the sunrise dottyback (P. flavivertex).

From the Persian Gulf, the neon dottyback (P. aldabraensis) is arguably the most beautiful member of the genus. It is orange with neon blue markings. This species has recently become popular with reef enthusiasts owing to its propensity for feeding upon bristleworms, a trait shared to some extent by the other Pseudochromis species. All the dottybacks are ideal inhabitants for aquariums in the 30-gallon size range, although only P. fridmani is sufficiently gregarious to tolerate others of its kind in the same tank. Look for more dottybacks to be offered in the future. There are at least 31 described species, and new species are still being discovered.

Neon gobies (Gobiosoma oceanops) were one of the first species, after clownfish, to be produced commercially. They are still available, though somewhat less popular than the larger members of the vast goby clan. Seaweed gobies, genus Gobiodon, include several species. Gobiodon citrinus, the citron seaweed goby, is perhaps the most widely available, although the clown seaweed goby (G. atrangulatus) is equally attractive. The former is yellow in color, while the latter is turquoise green with maroon markings. Either has the charming habit of perching motionless in seaweed or a branching coral head. Typically under 2 inches in size (although G. citrinus is somewhat larger), seaweed gobies are suitable for even very small marine tanks. There are many species of Gobiodon and Gobiosoma. No doubt several of these will soon be available commercially. Of particular interest are the red headed goby (Gobiosoma puncticulatus) from the Sea of Cortez and the limestriped goby (G. multifasciatum) from the Caribbean. The common names of these small species are adequately descriptive.

Like clownfishes, the dottybacks and gobies are easily maintained on a varied diet of small, meaty seafoods (brine shrimp, chopped shellfish, fish meat, etc.), supplemented with some plant matter. Diet is important for color maintenance in these fishes, so choose frozen foods with a good mix of ocean-derived ingredients.

In all, about 11 species of fish are in regular production at C-Quest, and the situation is similar for other, smaller hatcheries located throughout the United States. When I asked C-Quest president Bill Addison which additional species he would like to have, he responded that his favorites would be all the rest of the clownfish not now in production and all of the dottybacks, because, Bill says, “They have always been one of my favorites.” If Bill gets his wish, this alone would bring to over 50 the total number of marine fish species available through hatchery propagation. But the potential is even greater than this.

Successful rearing of marine fish through the larval stage (i.e., beyond the point at which their survival in captivity is wholly dependent upon successful laboratory techniques) has been accomplished for an impressive array of species. Commercial availability of these species has been largely limited by strong competition from cheaper, wild-caught fish. As hobbyists have become more concerned with issues of coral reef conservation, demand for tank-raised, rather than wild-caught, specimens is increasing. My recent correspondence with Bob Hix, president of the Marine Aquarium Societies of North America (MASNA), suggests that many members of the clubs MASNA represents would prefer to have tank-raised fish when they are available. With this in mind, consider what the tank-raised inventory might look like a few years from now.

Martin Moe made headlines in the hobbyist literature years ago with successful rearing of French (Pomacanthus paru) and gray (P. arcuatus) angelfishes at his Aqualife Research Corporation. Marc Clark of Aquatic Wildlife Company, Inc. was hard at work on rearing royal grammas (Gramma loreto) when I visited his facility in 1997. Forrest Young of Dynasty Marine Associates was successful in rearing yellowhead jawfish (Opistognathus aurifrons), although the project was too labor intensive to be a commercially viable effort. Each of these genera has species that are popular in the aquarium trade. Some command a very good price, such as the emperor angelfish (P. imperator), the blackcap basslet (Gramma melacara) and the other five species of Pomacanthus that are regularly imported.

Stan Brown of the Breeder’s Registry, a non-profit group that keeps track of successful captive propagation of marine fish and invertebrates, reports that the following fish families, in addition to those already mentioned above, have been documented as having been reared through the juvenile stage. Stan notes that not all, by any means, have been commercial successes, and that some reports have come from open system aquaria or research institutions. The list serves to demonstrate the great potential for the tank-raised market, however, and includes: hogfishes (Family Labridae, subfamily Bodianinae), comet groupers (Pleisiopidae), sea horses (Syngnathidae), cardinalfishes (Apogonidae), reef drums (Sciaenidae), spadefish (Ephippididae), dragonets (Callionymidae) and blennies (Blenniidae). If all the commercially important species in all these families were regularly produced, an entire store could be stocked with captive-propagated marine fish.

Commercial-scale cultivation of marine fish in hatcheries was a risky experiment less than two decades ago. Today, a hardworking entrepreneur can make money from marine fish aquaculture even in a location far removed from the tropics. As more and more species are added to the roster of captive propagation, the marine aquarium hobby achieves greater and greater promise as a truly mass market industry on a par with freshwater aquarium keeping.

Comments about this article can be sent to P.O. Box 9118, Knoxville, TN 37940-0118, or e-mailed directly to me.