Wondersea Marine Aquarium

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Captive production of Ornamental Marine Fishes
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Captive production of Ornamental Marine Fishes

As with the development of our species in going from being hunter-gathers of foods to their controlled growth and reproduction, marine aquaculturists have begun to make inroads in successfully breeding and rearing of marine fishes. Indeed, a few species (the Clown fishes, subfamily Amphiprionae and Neon/Cleaner Gobies, genus Gobiosoma) are largely produced in captivity nowadays, doing more than reducing correspondingly their wild-collection. Captive-produced marines, as with freshwater have proven hardier, more adaptable to aquarium conditions. They much more readily take prepared foods and are often specific pathogen free.

Though the vast majority (likely more than 90%) of marine fishes used for ornament are still wild-collected, there are great improvements in capture of healthy broodstock, knowledge of modes of their reproduction, induced and natural spawning and breeding, culture of useful foods, and overall husbandry techniques which foretell the possibility of captive production of any and all species.

Fishes are induced to spawn by altering environmental parameters, particularly temperature and photoperiod, and hormonal manipulation. These variables are generally constant for a given species, but vary widely amongst cultured fishes.

Spawning, Breeding:

Some fifty-four families of fishes include live bearing species that utilize internal fertilization with either no further nourishment from females (ovoviviparity) or placenta-like structures between their young and their bodies (viviparity). Forty of these fish families are cartilaginous fishes (sharks and rays) and the remaining marine ones of little notice (currently to marine aquarists). Additionally there are fishes that engage in internal fertilization, placing their sticky embryos at a later time. None of these species are either presently utilized by aquarists. Hence, we are almost exclusively concerned with spawning species, those that broadcast their sex cells into the environment when considering the captive production of ornamental marine fishes. 

History:

Early records at trials at culture of ornamental marine fishes likely don’t exist. Many "casual aquarists" of the sixties experimented with home and some commercial production of Clown fishes. Their accounts are anecdotal at best. Friese (1971) reminisces over hobbyist accounts of partial successes of breeding, rearing marine fishes (seahorses, pipe fishes, some gobiids, a few pomacentrids) in the 1960’s, and cites "recent" work to that time on multigenerational breeding done at the Wilhelma Aquarium in Stuttgart, Germany by Dr. W. Neugebauer of Hippocampus, Dunckerocampus and Amphiprion spp.

Hoff (1985) relates the early beginnings of commercial ornamental marine fish culture in the United States with his involvement with Instant Ocean Hatcheries (1974-1985), Aqualife Research (moved to Walker’s Caye in the Bahamas from Florida, founded by Martin Moe in 1972, who is still engaged in active research) and Sea World (San Diego, run by Chris Turk) who have all ceased production.

These early ventures likely failed commercially as Hoff states for Instant Ocean Hatcheries, due to too much overhead cost. They all were able to sell all (mainly Clown fishes) they could produce.

Current commercial facilities in operation include Tropic Marine Centre in the U.K., ORA (Oceans Reefs Aquariums) in Florida in the U.S.A, and C-Quest in Puerto Rico, Mangrove Tropicals (clowns and Dottybacks) and Ocean Rider (seahorses), both of Hawaii and South Australian Seahorse Marine Services (Hippocampus abdominalis). Experimental/university labs that are engaged in research involving marine pet-fish species include The Aquarium Complex/Marine & Aquaculture Research Facilities Unit (MARFU) at James Cook University in Queensland, Australia, Guam Aquaculture Development & Training Center, Hofstra University Marine Laboratory in Hempstead, New York, various Sea Grant locations in the United States (principally in Hawaii),

Sidebar: Marine Fishes Produced in Captivity: 

 Principal Ornamental Fish Species Under Production:

Clownfishes, Family Pomacentridae, Subfamily Amphiprionae 

Gobies, Family Gobiidae: Though many species of gobies of this large family have been captively spawned and reared, only the Cleaner Gobies, principally of the genus Gobiosoma are presently commercially produced. Along with the Clownfishes the cleaner gobies make up the bulk of the ornamental marine fish culture market.

Dottybacks, Family Pseudochromidae: Dottybacks can be very aggressive when wild-collected. As with many cultured freshwater fishes, captive-produced generations are much more easygoing.

Cardinalfishes, Family Apogonidae: A few species of this male-mouthbrooding family have been spawned and reared in captivity. As of now, the only commercially valuable species under culture is the Banggai Cardinal.

Seahorses and Pipefishes, Family Syngnathidae: These ever-popular aquarium fishes have dismal survival histories coming from the wild that are entirely reversed with captive-produced stocks. TMC of the UK has "closed the loop" producing successive generations of some species of pipes, and Ocean Rider of Hawaii is enjoying great success with production of a few seahorse species. Institutions like public aquariums have had success with breeding and rearing more than a dozen species of horses to date.

Production Considerations:

Several critical elements must come together in aquaculturing captive ornamental fishes. Selection of suitable species, securing of broodstock, conditioning, the actual physiology of gamete production and release through environmental and/or hormonal manipulation, provision of grow-out facilities and supplying of appropriate foods.

Species Selection:

Criteria for selecting potential species for captive propagation include compatibility, color and markings, size, inherent hardiness to captive conditions/shipping and handling, and interesting behavior.

Compatibility is key as there is a huge range of desirable behavior amongst reef fishes. Some are absolute terrors that even with successive generations of captive breeding are proving troublesome. The best example here is Pseudochromis steenei, the Lyreback Dottyback. This fish is likely responsible for many many aquarists outright quitting the hobby due to its predaceous nature.

Broodstock:

Many breeding attempts are made impractical if not impossible by the selection of inopportune broodstock. Sufficient numbers of potential spawners or breeders must need be secured to afford the luxury of their controlled upbringing and possible sacrifice to determine viability.

Conditioning:

Keeping broodstock in optimized, stable environments is absolutely key to captive breeding programs. As such culture facilities do their utmost to properly house their breeders. Most are kept in recirculated, centralized filtered tanks, with automated controls for water quality, including dosers for values like pH, probes for temperature, and regular testing for metabolites like nitrate, phosphate.

Diet:

Bogenschutz and Clemens (1967) were amongst the first to scientifically explore links between nutrition and gonadal development. They demonstrated gonadal regression induced by restricted diets, accompanied by an inversion of the basophil/acidophil ratio of the mesoadenohypophysis and a reduction of gonadotropin content. These conditions were reversed with adequate food. These authors stressed the interplay between photoperiod and diet and pointed out that optimum benefit from photoperiod manipulation can be overridden by poor diets.

Often special foods with vitamins, HUFAs (Highly Unsaturated Fatty Acids), and minerals added are specifically made, tailored to the individual species. Some excellent businesses like England’s Tropic Marine Centre use this opportunity to tie in sales of their proprietary frozen food line (Gamma Foods). Use of dried foods and relatively hollow nutrient content foods like adult brine shrimp is discouraged for conditioning breeders.

Disease Prevention:

As part of a working plan of maintaining broodstock attention must be paid to preventing the introduction of disease-causing organisms. To mention them again, TMC (Tropic Marine Centre) should be cited for the exclusion of such pathogens. Through careful quarantine, use of antibody treatments, their entire facility is specific pathogen free.

Gametogenesis & Reproductive Behavior:

Marine fishes produce and release sex cells based on maturity of the individuals, their nutrition and overall health, triggered by cues from the environment (temperature, light/dark duration, tides, presence of conspecifics, mates…) that in turn influence their hormonal/endocrine systems. Along with endocrine control there is a steady, intimate, more sudden interplay of the fishes’ nervous system, feeding in and coordinating activity through their eyes, hearing, lateralis system, senses of smell, and memory.

Conditioning and triggering of actual spawning involves combining knowledge of modes of reproduction, social factors such as sex ratios, environmental manipulation and possibly direct/exogenous hormonal administration.

Hormonal Manipulation As An Aquacultural Technique:

All fish behaviors are hormonally mediated, with much the same hormones, pathways as higher vertebrates. Hormonal manipulation of heretofore "difficult" species to reproduce involves the injection of exogenous hormones (pituitary extracts, HCG/Human Chorionic Gonadotropin, PMSG/Pregnant Mare Serum Gonadotrophin among other preparations.) intracoelomically (into the body cavity), intramuscularly (into the muscle), and in rare cases intracranially (into the brain) as has been done with caviar-producing Sturgeons.

Though not commonly employed in captive pet-fish production, widespread use of hormonal manipulation has allowed the breeding of many aquatic source protein fishes for human consumption. Hormones are slow-acting chemical messengers. Along with the faster acting central nervous system the tissues producing hormones (the endocrine or "crying within" system) serve to moderate, direct and sustain the physiology of all animals and plants. Combined with environmental manipulation, exogenous hormone administration can be used to provide seed all year long rather than rely on wild-collection of seasonal broodstock or young.

Gonadotropins are a class of hormones that instigate the production, development and release of sex cells. Hypophysation involves the injection of gonadotropins from one animal into another to bring on the physiology and/or behavior of reproduction. In practice with fishes, sometimes sexually-ready broodstock is sacrificed and their pituitaries (part of the brain that produces gonadotropins) utilized alone, or with mammalian-derived hormones or with these alone to cause changes in parental stock gametogenesis and sex-cell release.

Issues like standardization of dosage, determination of maturity of recipient fishes and nutritional requirements particularly need to be further explored for ornamental fish hypophysation. The first use of hormonal manipulation in fishes was in 1930 by B.A. Houssay of Argentina, who induced premature birth in viviparous fish by injecting pituitary glands recently removed from other fishes.

The author is aware of the use of hormonal manipulation being used experimentally on marine fishes for the ornamental trade, their use in marine food-fish production, and continued use in freshwater pet-fish species like Arowanas (Scleropages species) and Pangasiid Catfishes. However, as ongoing protocols, only environmental manipulation (principally temperature and photoperiod) are utilized to standardize, induce seed production and spawning. Bear in mind that what is being "manipulated" by changing environments are the broodstock’s endocrine systems themselves. That these are variable and specific to species. The environment in all its elements (nutrition, social inputs, light, disease-causing organisms…) is the source of phenomena determining hormonal secretion.

Environmental Manipulation:

The environment is the source of phenomena determining hormonal secretion. Several factors, photoperiod, temperature, metabolites, pheromones, light strength and temperature shock control release of gonadotropins, which in turn induce gamete production and concomitant reproductive behavior. Reproduction may occur out of season by manipulation of temperature and photoperiod alone.

Studies such as Moyer et al. (1993), and compilations like Thresher’s Reproduction in Reef Fishes (1985) point the way to how seasonality, particularly temperature and photoperiod influence natural reproduction. Additionally, social structure (inter- and conspecifically) plays a role in many species studied (e.g. Thalassoma spp., Warner and Hoffman (1980)). All fishes have discernible influences, cues that coincide with environmental changes… typically tied in with the absence of predators of spawners and/or their young, availability of natural foodstuffs, reproduction of other life forms.

The reproductive behavioral plasticity of many important cultured species is demonstrated in Clownfish culture. These damselfishes are always found in intimate association with actinarian hosts (sea anemones) in the wild. In captive culture they are almost always kept and bred without these animals, and do reproduce very readily on provided hard substrate surfaces.

A further example of improved culture through just manipulation of environmental factors is offered: The Ayu (Plecoglossus altivelis) , a smelt-like fish cultured in Japan during the Summer months, normally spawns in Oct.- Nov., after which most of the fish die. Due to lower water temperatures that time of year, it’s difficult to maintain live food organisms in adequate densities in rearing ponds to feed fry. An adjustment of photoperiod resulted in successful acceleration of sexual maturation (August), enabling rearing of fry when natural food was abundant. Spawning was also delayed to prolong the life of adults. The light period was extended to 18 hours per day with artificial light (Aug.- Oct.). Reproduction was retarded and adults were marketed out of season in Feb. (Kuronoma 1968).

As an interesting follow-up, recent trends in culture of the Ayu now include successful transfer of genetic material from rainbow trout. Trials have double their weight and increased length per time by a factor of about 1.3 (Cheng et al. 2002).

Temperature:

The relative importance of temperature as an instigator of reproductive physiology and behavior varies per species, investigator and experiment, but all agree a certain range and lowering or elevating optimizes results. Due to the nature of commercial enterprises, much of actual technique and applied values is of proprietary nature with ornamental marine fishes. Some unrelated species examples include Smiglieski (1975) who stated that temperature was the controlling factor in his work with flounders. Yamamoto et al. (1966) observed spermatogenesis in goldfish (Carassius auratus) below 14 C. and accelerated spermiation above 20 C.

Often, if much temperature fluctuation occurs reproductive behavior will cease (Kaya 1973, Lofts et al. 1968). As most marine fishes are summer spawners, a steady increase in photoperiod (to 14-16 hours per day) and temperature (25-27 C., 77-81 F.) can be utilized to stimulate repeated spawning. For some fishes (e.g. Clownfishes) such manipulation can insure spawning every two or so weeks, for other species up to a three month cycle of condensing seasonal changes is required.

Haydock (1971) has observed temperature threshold below which gulf croaker will not hydrate or ovulate. For each species or sometimes race there are limits, both high and low, and rates of change in temperature which will eliminate reproduction physiologically and behaviorally.

Light:

As with temperature, there are optimal amounts of strength, quality and duration of light in relation to reproductive events. On work with bluegill sunfishes it has been found that a longer photoperiod of 16L/8D vs. 8L/16D induced a better gonosomatic index (relative weight of gonad versus body; G.S.I. = ovary wt./total body wt. X 100). Males were more aggressive, dug more nests and fertilized more eggs.

Hoar (1969) sums up the effect of longer photoperiods by stating that they stimulate secretory activity of the anterior pituitary gland, inducing presexual behavior. The pituitary Lutenizing Hormone activates interstitial tissue of the gonads which produce gonadal steroids which dominate sexual phases, taking complete control during parental phases (Kaya & Hassler 1972). Other investigators have shown that elevated temperature and prolonged photoperiod together increased gonad maturity in green sunfish, Lepomis cyanellus.

Other Factors:

Photoperiod and temperature have received most attention and are generally considered to be of greatest importance in inducement of sexual maturity and spawning (Jhingran 1969). Other factors such as the effects of other environmental stimuli; meteorological (rain, floods, etc.) and water conditions (pH, ammonia, carbon dioxide, turbidity…), specific gravity (Walker and Herwig 1976), on controlled breeding of food and ornamental fishes has been investigated. In several species, the presence of con- and/or heterospecifics is important. In bluegills it has been found that when males are present, the most aggressive female has greater ovarian development. Another application of environmental control is employed in mullet culture in Israel. By keeping adult mullet in freshwater ponds, denying them access to the sea where they migrate to spawn, fish-culturists are able to extend the spawning season (Jerome 1975).

In summary, investigations into seasonal cues in the wild that bring on pre-spawning conditioning and spawning have proven fruitful for artificial culture of ornamental marines.

Criteria for Judging Sexual Readiness: Biological and Chemical Assay

Some species of ornamental fishes are raised in groups and maintained as breeding pairs (e.g. Clownfishes, Dottybacks, Gobiosoma gobies) or harems (dwarf angels of the genus Centropyge), while others are placed together only for the purpose of spawning. Several methods are applied towards determining sex and sexual maturity of spawners. For most of the current ornamental marine fishes under culture, formation of breeding pairs is done by maintaining numbers of individuals in larger (tens to hundreds of gallons) systems over months time, having them naturally "pair-up", then moving the pairs to small breeding tanks, generally moving them rather than their spawn and media it’s attached to to replicate containers.

In the use of hormonal manipulation it is often necessary to sacrifice some of the broodstock to assess their reproductive stage. Injection of hormones in an otherwise unripe adult will not generally induce gametogenesis or ripening of eggs if the breeders are otherwise unconditioned. Determination of spawning-readiness is sometimes associated with color or marking changes, distension of the body. There are chemical assays of body fluids which can be used as guides of readiness, but these are not as commonly employed as much as simple hand-stripping of gametes, their mix and microscopic examination as a guide to broodstock fitness.

Spawners/Spawning

Spawning entails two strategies, either dispersement of eggs into the environment directly (pelagic) or placement of eggs (benthic) and directed spraying of spermatozoa to fertilize them. Almost all cultured species, indeed nearly all bony fishes have a pelagic larval developmental stage, a delicate time of days to weeks, sometimes months when they are moved about by ocean currents, hopefully avoiding predation and finding adequate forage.

Due to their greater ease of rearing, most cultured marine aquarium fishes are benthic spawners, with the tube-mouthed fishes (seahorses and pipefishes) and the mouthbrooding jawfishes and cardinalfishes being specialized cases. These fishes provide parental care, and though their spawning numbers are lower than broadcast spawners, their young hatch out in much more advanced stages of development, accepting larger food items and therefore enjoy higher survivability.

An example of Gobiosoma gobies: A few inches length of 1/2 inch PVC pipe is placed on the bottom of each pairs enclosure to serve as a spawning substrate. Eggs are adhered to the inside of the pipe by the female and fertilized by the male. Males guard the deposited, fertilized eggs until hatching, typically in 3-7 days, depending on species and temperature. Methods vary with Gobiosoma hatching protocols. Some culturists leave the egg mass with the male in attendance till the young are free-swimming, removing the male at that time. Others induce hatching by gently pipetting water over the egg mass when the embryos eyes become fully pigmented and the yolk sacs are no longer visible.

About Collection of Wild Spawn, Larval Fishes 

If access is ready, there is a possibility of collecting wild produced larvae. This has been done for several species, including one of the two native pomacentrids of California, the Garibaldi, Hypsypops rubicunda, by the author. Guarded nests were combed of their developing eggs and young, transported in closed jars to the lab and grown out with varying degrees of incidental mortality. Unfortunately many young fish were found to be parasitized by intestinal nematodes.

Collection and rearing of post-settled larval ornamental marine fishes is a successful business in French Polynesia at present. Small fishes near to settling stage are caught in fine nets at night time on the reef and transported to land-based grow-out facilities. Wild-collected seed and larval sources bear the infectious and parasitic disease difficulties of larger wild-collected individuals, but have been shown to adapt with far greater facility to captive conditions.

Pelagic eggs and young can be collected with plankton nets (300-500 micron mesh) drawn slowly through the water or held stationary in currents. This is assuredly a "shot-gun" approach that leads to a very large, variable mix of species.

Rearing of Larvae, Young:

Massive mortalities in the wild are the rule for initial few hours to days of fish larvae and young. For the majority of species ninety some percentiles are typical within the first few days, with gametes, embryos and fry being swept out to sea or being consumed by predators. Understandably, conditions are much more constant and less dangerous in captive culture. With provision of ready nutrition, an absence of predators, the majority of young per batch will hatch out and develop.

Culture of Foodstuffs:

Toonen (2002) rightly points out that suitable food availability is key to successful aquaculture of marine animals. This is likely the largest source of mortality for cultured (and wild) reef fish larvae and fry. Having appropriate food organisms and prepared foods present almost continuously is required for optimal growth and survival.

Here again, there has been syncretization in wild studies such as Riley & Holt (1993) in studying gut contents of larval fishes as well as documented trials and errors in trying to grow and feed cultured foods (principally algae, rotifers, crustaceans, e.g. Hoff, 1999.) to cultured fish larvae. The road to discovering and providing proper, palatable foodstuffs at appropriate intervals and attractive formats has been a long and expensive one in many cases.

Plankton Culture

Various species of phyto and zooplankton are cultured to feed different species of larval fishes, often in a dual step fashion, growing phyto-plankton to feed the zooplankton to feed the fishes in turn. The plankton cultures are typically kept under controlled conditions (light, temperature) in separate rooms to prevent contamination. Some examples of commonly employed cultured live foods are detailed below.

Of the microalgae Isochrysis galbana can be grown under fluorescent lights per Hoff and Snell (1987). Isochrysis is used both as a water conditioner and as food for zooplankton.

A common rotifer, Brachionus plicatilis, is often used as a first food, often followed by nauplii of the Brine Shrimp, Artemia salina. Rotifers can be cultured in as small as 10-gallon aquaria at a salinity of 25ppt, on a combination of Culture HUFA (tm) from Salt Creek, Inc., and concentrated Isochrysis paste from Reed Aquaculture, inc. Culture densities typically range from 100-250/ml.

Certainly key in fish culture worldwide is the hypersaline crustacean called Brine Shrimp, Artemia salina. Rather than having to collect and hold them as food items, Artemia cysts are often decapsulated with household chlorine bleach that then can be refrigerated in a saturated salt solution, and hatched as needed.

Provision of Foodstuffs:

It’s not enough to simply know and have on hand nutritious foods for cultured ornamental fishes. Their actual delivery in palatable formats, in sufficient concentration, at appropriate times is also critical. For the first few weeks of Clownfishes lives they require frequent (a dozen or more times per day) administration of nutritious foods where and when they metamorphose into small fishes, ultimately "settling", otherwise being more mobile than prevailing water movement.

Foods, either live and/or prepared should be fed several times daily, ideally on a continuous "as-needed" basis, and reciprocally never to excess. Various devices have been devised for automatically supplying these foods, from computerized peristaltic pumps to automated flake food feeders, to simply pinching low-fat dry foods between culturists’ fingers. A survey of the literature finds that feeding per species, age and facility as few as three times to as many as fifteen times daily to cultured young.

Grow-out Facilities:

Larval Rearing

Larval fishes have little tolerance for environmental stress; therefore culture systems must be made to provide optimized and stable conditions. Metabolites, particularly ammonia have been shown to decrease vitality, resulting in slower growth rates and death. Water quality, particularly temperature and salinity are necessary to match with new water. This can be achieved through the use of large amounts of recirculated water or close matching through pre-mixed and stored change water.

As gametes, embryos and larval fishes suffer high mortalities in being moved, parent stock is often stripped or otherwise removed rather than their young. For brooding species like Clownfishes and Gobiids this point of moving the parents occurs when the young are free-swimming.

A rearing protocol for Gobiosoma gobies is given below as an example:

In anticipation of hatching, 10-gallon larval rearing tanks are filled with synthetic seawater (Instant Ocean) at a salinity of 30 parts per thousand (ppt), gently aerated through via an airstone. Subsequently 1 liter of concentrated Isochrysis along with approximately 40,000 rotifers, (enough for a concentration of 10 rotifers/ml. are added. Post hatching, rotifer concentrations are estimated daily by removing 1 ml of water and counting individuals in a depression slide, using the 40x magnification dissecting microscope. 1 liter of Isochrysis is added to the tank daily, and rotifer concentrations are maintained at approximately 10/ml.

On or around day15 post-hatch, newly-hatched nauplii of Artemia are introduced to the diet. After a 5-10 day overlap period, the fish larvae are fed Artemia exclusively. All rotifers and Artemia are soaked in a commercially-prepared suspension of highly unsaturated fatty acids (HUFAs) for 12-16 hours prior to feeding. Once the rotifer diet has been completely replaced by Artemia, Isochrysis alga is no longer added, and a pre-cycled air-driven foam filter is placed in the tank to help maintain water quality. Additionally, a 50% water exchange is performed every 3-4 days by siphoning water out through a section of flexible air tubing inserted into a 500-micron Nitex screen sleeve submerged in the tank. The sleeve prevents larvae from being siphoned out. Replacement water is then siphoned back slowly into the tank.

Gobiosoma reach metamorphosis around 30 days post-hatch. Metamorphosis is defined in these species by a rapid accumulation of color (not useful as planktonic larvae) and settlement from a pelagic to a benthic mode of existence. Around the time of metamorphosis, dry feeds are introduced to the diet and becoming exclusive foods within 3 weeks. Juveniles are accumulated from various rearing tanks and consolidated into 29-gallon tank systems.

Grow Out Tanks:

Though food-fish are cultured in open to semi-open systems, pumping fresh seawater to them and either allowing used water to flow back or to be partly (semi-open) filtered, aerated and recirculated for re-use, almost all ornamental marine fish culture involves closed or completely re-circulated water systems. The upside to closed systems is the greater control one has over initial and ongoing water quality. With such re-used water there is little chance of introduction of parasites, pests or pollution. The downside is the expense of its making and/or transport and manipulation (heating, filtering, pumping).

Water in grow out systems must be moved very gently. Particularly the first week or two of life is a delicate time with all but the finest of air-bubbles able to outright kill small larval fishes. Hence, either slow moving water introduced through fine screens and exited through fine screens (to keep young fishes in) or very fine air-stones are employed for water movement and aeration.

Some investigators have used as little as ten percent daily trade-out of culture water in larval grow out (Siddall 1979), but if good quality water of equal temperature and specific gravity can be assured there are many benefits that accrue from larger daily change-outs. Notable improvements from dilution of metabolites include improved growth rates, vitality and reduced intraspecific aggression.

Size of grow-out vessels is critically important. Due to problems of moving young fishes, these grow-out containers must be large enough to accommodate the batch of young through at least the first six weeks or so of development. Houde (1973) proposes minimum volumes for some pelagic species being twenty gallons. Rationale for size is offered for allowing adequate gas exchange (at 3-7 larvae per liter, 11-27 per gallon), reducing aggressive interactions, diluting growth-limiting pheromonal metabolites (Yu 1968). For fishes of about ½" total length a maximum density of two per gallon is suggested by Young (1995).

There are many designs of culture and grow-out containers, some involving elaborate curved tanks and screens. For many operations, simple rectangular glass aquariums of twenty or more gallons work fine, being readily available, inexpensive, easy to move and clean. Fitting these with a simple airstone and some mechanism for water changing works for most species under culture.

Maintenance:

As per hobbyist use of synthetic saltmixes, these must be made up, aerated and stored for several days ahead of use to ensure overall stability. For closed-system arrangements, the water changed out from larval culturing systems can be used further for adult systems and food-culture facilities.

Often it is of benefit to keep phytoplankton blooms in the rearing tanks, such algae presence assuring improved survival and growth of larval fishes. The algae serve to remove metabolites, produce oxygen, diminish intraspecific interactions (possibly by simply decreasing visibility), feed zooplankton foods. Various genera have been employed for this purpose (Chlorella sp., Chlamydomonas sp. Anacystis sp.)(Siddall 1979). In actual practice, particularly when dealing with semi- to fully open systems, no specific measured amounts of concentrated algal culture are administered, but some added on a daily basis to render the water a light green in color.

Larval fishes must be examined often and closely for signs of intraspecific aggression or its manifestations (dissimilar growth et al.) and increased water changes, addition of décor (bits of coral, plastic to physically break up the environment) placed to reduce same.

The importance of avoidance of toxins cannot be overstated. Tanks should be cleaned and triply rinsed to assure removal of any contaminants. Workers should abstain from tobacco use, and be instructed on thoroughly rinsing of their hands and arms in advance of hatchery work.

To keep fishes off the bottom of culture vessels, feeding and therefore growing, some ambient lighting is supplied continuously in culture facilities. This is especially important in separating the young from the inevitable accumulated detritus on tank bottoms, and the ill-effects of high bacteria counts associated with it (loss of growth, health, life)(Young 1995).

Diseases, Pests and Abnormalities:

Compared to the wild, captive-produced ornamental fishes have spectacular hatch out and larval survival rates. Nonetheless, infectious disease and genetic and developmental defects can play significant roles in incidental mortalities and loss of salability of stocks.

Certain bacteria (Pseudomonas, Vibrio spp.) are likely omnipresent in culture systems. Early efforts in culture of ornamental fishes employed antibiotics (e.g. penicillin, streptomycin, Chloramphenicol, sulfamerazine) to retard their growth. Later methods of bacterial population limitation include ultraviolet sterilization and ozone use. Special care must be exercised in employing antibiotics in systems relying on biological filtration in closed settings, as these compounds may cause a loss of nitrification partially or wholly.

There is a variable potential of introduction of parasitic disease and pests with the use of wild-collected planktonic foods. So much so that almost all facilities engage their own food-production facilities, keeping close controls on contamination of stocks.

Early (1960’s-80’s) culture of marine ornamental fishes showed a definite resistance in acceptance by the trade all the way to consumers on the basis of wild-fishes larger sizes, greater coloration, and a decided percentage of captive fishes with physical deformities (bent mouths, shortened unpaired fins) and markings (incomplete bars on Clownfishes) due to environmental trauma (thermal and osmotic shock, high metabolites, contact with culture vessel walls). Happily, these abnormalities have been largely solved, and the demonstrated greater survivability of captive produced fishes has shown them to be much better purchases than wild-collected specimens.

Benefits of Captive-Produced vs. Wild-Collected Specimens:

An assured shortcoming element of aquacultured fishes has been their apparent higher cost through the chain of custody/supply. What good are a ready supply of captive-produced species when wild-collected ones that appear the same or better color, size, behavior-wise are available at lower cost? With improvements in culture, changes in law (national and international), freight costs, and above all, sensitivity and awareness of retailers and hobbyists, there has been a groundswell movement to captive produced livestock. "Net-landed cost" of specimens, especially in consideration of "longer term" (months instead of days, weeks).

Similarly there are benefits in reduction of pressure on wild stocks extraction, avoiding corollary environmental damage during collection, loss of life of "by-catch", and very importantly, near absence of infectious and parasitic disease. Before the advent of cultured Clownfishes it is likely that some 95-58 % mortalities of wild-collected stocks occurred within a month of their capture. This figure has likely been inverted, with the vast majority of captive-produced Clowns living for a month or more in aquarist’s tanks.

Cloze:

Many other species of fishes have been successfully produced in captivity, croakers (family Sciaenidae), most of them for human protein markets.

With increased interest in captive-produced ornamentals, progress in their food culture, gained knowledge in natural history and husbandry techniques there will likely be few "hold-outs" in the spectrum of successful captive-bred and reared fishes in the future. This progress will further assure captive success in succeeding generations by aquaculturists and enhanced longevity in aquarium keeping of these species. It is hoped that with much more captive-adaptable (more readily feeding on prepared foods, absence of pathogenic disease, reduced shipping trauma, eliminated wild-collection damage) that captive-produced ornamentals will quickly grow to supplant wild-collected specimens.

Bibliography/Further Reading:

The Breeder’s Registry: http://www.breeders-registry.gen.ca.us/

Anon. 1984. Conditioning and spawning of marine fishes. Part I: Adult pairs, SeaScope v.1, Spring 1984, Part 2, Larval foods, Summer 1984. 

Anon. 1984. Food culture for marine fish larvae and filterfeeders. SeaScope v. 1, Summer 1984.

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Cheng, Chao-An, Kuen-Lin Lu, En-Lieng Lau, Tse-Yeng Yang, Chiou-Yueh Lee, Jen-Leih Wu & Chi-Yao Chang. 2002. Growth promotion in Ayu (Plecoglossus altivelis) by gene transfer of the rainbow trout growth hormone gene. Zoological Studies 41(3): 303-310 (2002).

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