Raising marine ornamentals in captivity principally is providing the right nutrition and environment for:
- Adults to produce quality eggs (Broodtock Care).
- Larvae to survive (Larval Rearing).
- Juveniles to grow (Juvenile Grow-out).
Ideal culture candidates are species that spawn routinely and voluntarily and have large larvae that can be raised in a short time to juveniles on easily cultured live foods. Being familiar with the basics of Reef Fish Reproduction will help to better understand this section.
The purpose of keeping broodstock is to obtain a proximate and constant production of quality, fertile eggs. Most damselfishes, dottybacks, basslets, hawkfishes, blennies, pygmy angelfishes, cardinal fishes, wrasses, triggerfishes, anthias, gobies, seahorses and ornamental crustaceans will naturally spawn in captivity if the correct conditions are provided.
Broodstock systems are single or multiple tank systems designed to provide the optimal environment (space, hiding, water quality) for good health and spawning conditioning of the adults. Commonly, numerous glass aquariums are connected with good central filtration. Each tank has aeration and water flow-through and is set up with a bare bottom and only the necessary hiding and spawning structure.
Selection and Pairing
Proper selection of healthy individuals that are or can be paired is the first important step to breeding marine ornamentals. Mated pairs (those that have previously mated) are ideal but not often available. Species can be paired based on sexual differences, such as color, size and external morphology and behavior or their ability to change sex. Most often, when placing several juveniles or sub-adults together the largest will develop into the dominant sex.
The value of quarantine for disease prevention cannot be overstated. Newly acquired fish or crustaceans may carry disease and may infect valuable, healthy, broodstock. They are therefore kept separately, in a tank or system, for three to four weeks where they are closely observed and treated with medications for possible disease outbreaks. Pair bonds may also be further established during this period.
Maintenance and Conditioning for Spawning
Many marine ornamental species that are paired and in good health will naturally spawn in captivity when correctly conditioned. Such conditioning means providing the proper quality and quantity of foods, the right lighting and temperature, optimal water quality and the appropriate surroundings (tank size, spawning and hiding structure). Often times these are determined by replicating the conditions a species experience in the wild during its spawning season.
Hatching Of Eggs And Transfer To Larval Rearing
The hatching methods employed by farms depend on the spawning strategy of the species they are raising. Knowing the egg characteristics (demersal or pelagic, size); spawning location, time and frequency; type of incubation (if any); and egg development period are important to develop the right hatching procedures. Eggs are less fragile than larvae and, whenever possible, are removed from the broodstock tank and incubated in the larval rearing tank before they hatch.
Marine fish and crustacean larvae are usually very fragile organisms and have specific nutritional and environmental requirements that change frequently and are often difficult to provide. This makes larval rearing the most critical, time consuming and complicated phase of the culture process. The length of the larval phase and the capabilities of larvae at hatching depend on the species. Obviously, species that have well developed first feeding larvae with a short larval phase are better culture candidates. Clownfishes and dottyback larvae can swim and feed at hatching and complete their larval phase in about 15 days and 30 days, respectively. The main goal of the culturist is to maximize survival. The aspects to the rearing process are as follows:
Live Food Production
Marine ornamental fish and crustacean larvae are usually raised on live foods to ensure high survival and growth rates. The most common live food employed are marine rotifers, Brachionus plicatilis, and brine shrimp nauplii, Artemia salina. Wild plankton and/or suitable marine copepod species are often employed for more difficult to raise larvae. Rotifers and brine shrimp nauplii are ideal larval foods because they are easy and cheap to produce in large quantities; they have the right size and movement as a prey organism; and they can be nutritionally enriched if needed. Rotifers are usually mass cultured on microalgae or yeast while brine shrimp nauplii are hatched out from cysts that can be purchased in quantity.
Larval Tank and Set-Up
Marine ornamental larvae are usually reared indoors under controlled artificial (fluorescent) lighting and temperature conditions, although favorable outdoor conditions may also be used. Rearing containers can be anything from small, 10-gallon glass aquariums to large 1,000-gallon round, black tanks, depending on the species requirements, desired production quantity and amount of space available. Oxygenation and light circulation is created from airstones rather than water pumps to minimize damage to the fragile larval body. Commercial larval systems are usually outfitted with fresh saltwater inflow for optional water exchange. Outflows are surrounded with a large surface area screen, again, for protection of the delicate larvae.
Marine fish and crustacean larvae require frequent and ample feedings of nutritious, appropriately sized foods. A larva’s mouth size, hunting abilities, digestive capabilities and nutritional demands will determine the type of live food it will survive and grow on. Clownfishes and dottybacks are raised on rotifers, then brine shrimp nauplii and finally artificial foods. Ornamental crustaceans are usually cultured on brine shrimp nauplii from first feeding and additional artificial diets in the late larval phase. Sea horses are commonly cultured on brine shrimp nauplii and/or copepods. Difficult-to-rear reef fish larvae usually require copepods to survive.
Generally, both rotifers and brine shrimp nauplii are enriched with commercially available preparations of essential fatty acids, vitamins and pigments before being fed. Several feedings per day are normally required to maintain the specific food quantities and quality required for the larvae to survive and grow.
Maintenance and Treatments
Marine ornamental larvae generally do not tolerate environmental changes well and, depending on the species, require specific conditions. Water quality, lighting, temperature, circulation and turbidity are just a few of the important parameters vital to larval survival. Commonly, culturists add live micoalgae to the rearing water to calm the larvae (increased turbidity); improve their hunting abilities (optic effect of microalgae); sustain water quality (microalgae take up nutrients); and maintain the nutritional quality of the rotifers and brine shrimp nauplii (feed on the microalgae). In the beginning of the rearing phase, when the larvae are most fragile and water quality is still high, water exchange is minimal. As the larvae grow and become tougher and nutrients accumulate in the rearing tank, water quality is maintained by periodic and careful bottom siphoning/water replacement and later through constant but minimal water flow-through (if available).
Transfer to Juvenile System
Larvae are transferred to a grow-out system after they are feeding on artificial diets and have fully metamorphosed into juveniles. Most species are now robust enough to be netted.
The juveniles of most species are hardy and vigorous once they have been transferred and adapted to their new environment. The focus of grow-out is to maximize the growth and quality attributes (health, color, shape) of juveniles to market size. This period usually takes anywhere from two to four months, depending on species.
Juveniles systems are designed to handle large bioloads. Farms commonly grow out their juveniles in large tanks (100-10,000 gallons) located indoors or outdoors (climate permitting). The tanks require a high water exchange to maintain water quality. Three types of systems are used to accomplish this. Closed, recirculating systems maintain water quality by circulating the dirty, nutrient rich water through a large filtration system. Open, flow-through systems use a clean source of quality saltwater (for example a well), which is completely discarded after it exists the tanks. Partially open/closed systems discard only part of their water and recirculate the rest through central filtration. The type of system employed depends on water source available and the juvenile production quantities.
Stocking, Feedings and Maintenance
Juveniles are usually grown out at a stocking density between one and ten fish per gallon. They receive frequent (3-5x per day) and ample portions of nutritious feeds to optimize their growth, color and health. Tank siphoning, filter cleaning and water changes (if recirculation) are part of the maintenance routine.