Broodstock Conditioning

Breeding Potential

The breeding potential of Centropyge is excellent. Not only are they small, hardy and easily paired but those species that adapt well to captivity will often spawn without any special provisions. In fact, aquarium spawning is frequently witnessed by hobbyists and has been documented for more than 14 species.

In nature, the reproductive strategy of Centropyge is to produce a moderate number of small eggs, daily, over a long reproductive life span. However in captivity, egg production can be poor and random when the proper diet and environmental conditions are lacking. In my experience, there are a number of key criteria to consistently achieving consistent, large, quality, fertile spawns.

Tank Size

First off, consider the size and height of the spawning tank. A pair or trio of an average sized Centropyge species, like the Flame and Lemonpeel Angelfish, should be kept in a minimum volume of 50 gallons. Smaller species, like the Fisher’s Angelfish, need little more than 30 gallons. I have found that egg fertility greatly improves when Centropyge are given enough room during the final rise that culminates in spawning. Therefore, the height of the water column in all of my Centropyge broodstock tanks is at least 20 inches. As for infrastructure, I provide a little bland décor in the form of pots or tiles for hiding but also leave adequate room not to restrict courtship behavior. My best spawning results thus far have been attained in standard, 3-foot high 55-gallon drums and 4x2x2 foot, 120-gallon aquariums. Each of the aquariums contains two pairs separated by a divider.

Lighting and Temperature

Lighting and water temperature are important parameters when conditioning fish to spawn. As in all reef fishes, the reproductive cycles of Centropyge are closely tied to environmental cues. Warm water temperatures and long days induce gonadal maturation and reproductive behavior. Tropical species (example: C. flavissimus , C. bicolor and C. bispinosus) will spawn periodically throughout the year, while those experiencing seasonal changes usually have a distinct breeding season. For example, the Japanese Pygmy Angelfish, off southern Japan, and the Potter’s Angelfish, off Hawaii, only spawn in the spring and summer months when daylight exceeds 13 hours and temperatures are or rise above 26°C. During their spawning period Centropyge species reproduce daily. Courtship commences near late afternoon and culminates at dusk.

I provide a light period of 15 hours at 1-3 watts per gallon to induce reproduction . Light intensity is reduced during the last two hours to create a crepuscular effect, though this is not necessary once the fish begin to spawn regularly. Water temperatures are maintained near 28°C for tropical species and 26°C for sub-tropical ones. Winter-like conditions are created for 1-2 months every year by reducing the light period by 3 hours and temperature by 3°C. This change inhibits reproduction and gives my broodstock a well-deserved rest.

Nutrition

Providing the right nutrition is critical, not only to keep a pair healthy but also to obtain a good quantity of fertile eggs. In nature, Centropyge have a non-specialized diet, feeding primarily on algae, detritus and interstitial fauna. In the aquarium they should be provided with a balanced diet. Conventional aquarium foods such as frozen, chopped seafoods, quality flakes and pellets and commercial gel diets containing algae are adequate. I’ve had best results conditioning broodstock on 2-3 daily feedings of a diverse seafood gelatin diet, rich in vitamins, pigments and highly unsaturated fatty acids. Important ingredients include fresh fish and shrimp, fish roe, a multi-vitamin mix, spirulina and astaxanthin. In addition, I allow for ample growth of golden diatoms (brown algae) in the aquarium. Species that rely heavily on detritus and small benthic fauna in their diet (C. potteri, C. interrupta), are kept in tanks that are less frequently cleaned and set up with sand bottoms. The Japanese Pygmy Angelfish actually feeds directly on fecal material of other reef fishes in the wild.

Water Quality

Last but not least adequate water quality needs to be maintained. This means the system should have an established nitrogen cycle (no ammonia or nitrite and nitrate levels below 50 mg/L), a specific gravity between 1.020 and 1.024, (the lower end of this is more ideal), a pH near 8.2 and the appropriate water temperature and lighting (as discussed earlier).

Most of the system at my facility are connected and have central filtration. Some are isolated as individual systems. Each system is designed to be simple, efficient and easy to clean. The water is recirculated through a sump in which a 5 um bag filter removes particulates. Since the bio-load is small, a standard sand plenum provides ideal biological filtration. The plenums are either built into the sumps or tanks themselves. All tanks with bare bottoms are siphoned daily while those with in-tank plenums are cleaned once a month. A 50 percent water change is done every 2-3 months.

Barrel system (55 gallon) used to spawn Centropyge broodstock
Barrel system (55 gallon) used to spawn Centropyge broodstock

Egg Collection

The females typically produce between 300 and 2000 fertile eggs every night. Collecting pelagic eggs is relatively easy since they are buoyant. My broodstock tanks have surface outflows that spill into a collecting tank where the eggs are concentrated in a screened container over night.  In the morning the eggs are washed into a 1-liter beaker with fresh saltwater. Pelagic eggs that die during development will sink to the bottom as will any unwanted material, such algae or leftover foods. Healthy, fertile eggs remain buoyant and accumulate at the rim. These can then be carefully transferred with a pipette into the larval rearing tank before they hatch.

Sorting Centropyge eggs
Sorting Centropyge eggs

Larval Rearing

Culture Requirements

Thirty-six reef fish families reproduce by releasing eggs directly into the water column. These include popular aquarium fish groups such as the tangs and surgeonfishes, butterflyfishes, wrasses, hawkfishes, and all marine angelfishes. The larvae of most pelagic spawners, like the Centropyge, are difficult to culture.  Compared to the larvae of commercially propagated species (clownfishes, dottybacks and most gobies), Centropyge larvae demand a smaller, more nutritious and easily digested food source at hatching; are more sensitive to environmental changes (water quality, lighting, temperature) and require optimal nutrition throughout development; and take much longer to both reach and complete metamorphosis.

Breakthrough

In November, 2001 I closed the life cycle for the Fisher’s Angelfish (Centropyge fisheri), the first Centropyge to be raised in captivity.   Between 2002 and 2011, I intermittently produced C. interrupta, C. resplendens, C. colini, C. debelius and two hybrids C.fisheri x C. replendens and C. resplendens x C. argi for the aquarium trade. A limited number of C. fisheri, C. loricula, C. flavissima, C. multicolor, P. multifasciatus, C. argi, C. acanthops and C. joculator juveniles were also reared for research.

First closing the Centropyge life cycle and then developing a reliable rearing technology was accomplished through a number of small advances, both in the diet and the environment, which helped the larvae survive a little longer each time. The first of these was the discovery of suitable copepod species.

Copepods

Copepods are the largest class of Crustacea inhabiting nearly all aquatic ecosystems on this earth. They can be pelagic, benthic or even parasitic. Of the over 4,500 copepod species that exist, most inhabit the oceans, where they form an important link between algae and higher trophic levels. The typical copepod body is cylindrical and segmented and, like other Crustaceans, is divided into a head, thorax and abdomen.

Copepods reproduce sexually. Upon fertilization eggs are secreted into ovisacs, which are attached to the female’s first abdominal segment. Each ovisac can contain anywhere from a few to 50 fertilized eggs. The eggs hatch into nauplii that go through 4-6 stages and then become cepepodites. After 5 copepodite stages they metamorphose into an adult, which is final molt.

Marine copepods are an important food source within natural zooplankton communities, especially for marine fish larvae. First off, they are widespread throughout all oceans and can occur at high densities, blooming seasonally. Furthermore, most species have a very good nutritional profile. All ontogenic stages are rich in proteins, highly unsaturated fatty acids, most amino acids and pigments. In addition, they are rich in digestive enzymes. This helps digestion and assimilation of essential nutrients in species where the early larvae have poorly developed digestive systems. With adult species ranging anywhere from 0.5 mm to 5 mm in length and some nauplius species hatching as small as 40 um in diameter, they also have an ideal size range as prey. Finally, their jerking and gliding motion elicits a feeding response and makes them easy to capture.

The natural qualities of copepods make them a model prey organism for rearing marine fish larvae. Consequently, there has been considerable interest to bring them into mass culture. Unfortunately, this has not been economically feasible for many suitable species particularly those that produce the appropriate nauplii preyed on by smaller first-feeding larvae. The primary biological attribute that makes such species unsuitable for aquaculture is their long reproductive cycle, which being sexual, can take anywhere from one to four weeks to complete under optimal conditions. By comparison, rotifers, commonly used to grow marine fish larvae through the first few weeks, reproduce asexually in less than 24 hours. Furthermore, desired copepod species are more difficult to maintain in captivity than rotifers, demanding better water quality, cleaner conditions, more space, and more nutritious feeds. The main copepod suborders (and genera) of interest to aquaculture are:

  • Calanoid (Parvocalnaus sp., Bestiolina sp., Pseudodiaptomus sp., Acatia sp., Eurytemora sp., Calanus sp. Pseudocalanus sp., Gladioferens sp.)
  • Cyclopoid (Apocyclops sp., Oithona sp.)
  • Harpacatcoid (Tisbe sp., Tigriopus sp., Tisbenta sp., Schizopera sp., Euterpina sp.)

A First Food Organism

Over the years I attempted to raise Centropyge larvae with numerous live food organisms, including small strain rotifers and ciliate species. Success was limited until 2001 when I began experimenting with copepod nauplii. At the time I was working with Fisher’s Angelfish larvae. The superiority of the new food over ciliates and rotifers was immediately apparent. First off, the larvae were more active at first feeding and were frequently observed attacking the prey, something I had never witnessed before. A larva would swim up to the nauplius, wind up its tiny body into the characteristic S-shaped attack posture and strike. Their swimming and hunting abilities perceivably improved each day. Second, the body of nauplii-fed larvae increasingly reddened starting on day 5. Upon closer examination I found this to be the build up of tiny blood vessels. By contract, the larvae reared on rotifers and ciliates would gradually become darker and die by day 9. Third, larvae feeding on nauplii were growing close to 5 mm in length from day 4 through day 10. Those fed rotifer and ciliates died at the size they were on day 5, when their yolk was completely exhausted.

Copepods nauplii used to feed early stage Centropyge larvae
Copepods nauplii used to feed early stage Centropyge larvae

Larval Development

The 12 species (C. interrupta, C. resplendens, C. colini, C. debelius, C. fisheri, C. loricula, C. flavissima, C. multicolor, P. multifasciatus, C. argi, C. acanthops and C. joculator) and two hybrids (C.fisheri x C. replendens and C. resplendens x C. argi) reared for the 10 project have a very similar course of development (ontogeny) up to metamorphosis.

The eggs are tiny, averaging 0.7 mm in diameter, and hatch after only 16-18 hours at 27-28 ºC. At this time the larvae are nearly transparent, about 2 mm in length and very primitive, lacking eyes, a mouth, a digestive tract and functional fins. As the yolk sac gets depleted these develop. Three to four days after hatching the larvae are able to start feeding. Properly nourished larvae will undergo noticeable vascularization (blood vessel formation) during the first 2 weeks of development. This “reddening” only occurs if they are growing and healthy. 15 and 25 days after hatching the larvae start to laterally compress.

They then take on silver coloration and develop strong pigmentation along the dorsal area. Metamorphosis starts 45-50 days after hatching and, depending on the species, can last up to 50 days. A darkening of the soft dorsal and anal fins marks the beginning of this transitional period. As juvenile coloration gradually fills in, the larvae become more stationary and behave less erratically. At this time they can be transferred to a grow-out tank.

Development of a typical pygmy angelfish (example: Centropyge debelius)
Development of a typical pygmy angelfish (example: Centropyge debelius)