In the 1970s and 1980s, the dream of many fish farmers and hobbyists was to breed Dragon Fish successfully. Due to the high price of the fish (a Red Dragon about 30cm (12in) long fetches at least £1500 or approximately US$2500 in the open market), many farmers attempted to breed the fish in captivity but with little success.
However, the dream became a reality in 1981 when the then Freshwater Fisheries Laboratory (now known as Ornamental Fish Section) of the Primary Production Department (PPD) of the Ministry of National Development, Singapore, succeeded for the very first time in breeding the Green Dragon variety in captivity.
Since then, Dragon Fish of the three types (Red, Gold, and Green) have been bred in captivity on several farms in Singapore, Malaysia, and Indonesia. However, the farmers were not allowed to sell their Dragon Fish as the species is placed under Appendix I of the endangered list of species by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (see here).
Any trade in the fish was restricted to captive-bred second filial generation (F2) specimens derived from farms which had demonstrated capability in breeding the species to at least the F2 generation and obtained approval from CITES.
This situation changed in 1994, when a commercial farm in Singapore, with the assistance of the PPD, successfully documented the production of an F2 progeny of the Dragon Fish and subsequently registered with, and obtained approval from, CITES to trade in the fish. This farm became the first in the world allowed to buy in all the three varieties of Dragon Fish. To date, a total of 11 farms in Singapore, Malaysia, and Indonesia have obtained approval from CITES to trade in the Dragon Fish.
This chapter describes the technology practiced by PPD and the commercial farm in breeding the Dragon Fish.
Pairing the fish
To breed Dragon Fish, it is important to understand their spawning behavior.
Dragon Fish spawn in pairs. In their natural habitat, it is relatively easy for the fish to select their partners and form pairs. In the captive environment, however, it is critical to provide the necessary conditions for the fish so that pairing can take place quickly. Keeping several fish in a large pond provides just such an opportunity for the fish to select their partners more readily.
One should also choose fish that are compatible, both in size and age. The difference in age (and, hence, the size) should not be greater than three years. A sex ratio of one male to one female should be kept in the pond to enhance the chances of pairing.
If only two fish are held together, as is often the case if home aquaria are used, matching may depend on whether the fish have been correctly sexed (sometimes it turns out that both are of the same sex) and, if properly sexed, on whether the individuals are sufficiently compatible with each other to pair up. It is, therefore, not uncommon to find eggs in an aquarium, but these will be unfertilised because the female has not been mated.
To match a pair of Dragon Fish successfully in an aquarium is like winning a lottery! This explains why, while there have been many records of successful breeding to great ponds, there is only one published record of successful breeding in an aquarium in Japan in 1989 (see here and Bibliography).
It is not easy to differentiate the sexes in Dragon Fish as they all look more or less the same externally, there being no morphological differences between the males and females. It takes a very experienced farmer to sex the fish and, even then, he may not be accurate all the time.
Sex differentiation of Dragon Fish is based mainly on the body shape and the mouth (buccal cavity) size of the fish. A male fish usually has a more spindle-shaped and slimmer body, and shallower body depth than the female fish, while its mouth is deeper and wider than that of the female. A brooding male can be recognized easily by its conspicuous brood pouch, which is used for holding its eggs and, later, the writhing young.
Water Quality Management
Optimal water quality conditions should be provided for the breeding population, and good water management is a fundamental element in any successful breeding program. But what are the optimal conditions and what constitutes good water management?
An essential condition is that the pH of the water is maintained within the range of 6.0 to 7.5. This corresponds to the pH of the water in the Dragon Fish’s natural habitat.
Another important condition is that dissolved oxygen is maintained at more than five parts per million (ppm or mg/1) at all times. Oxygen availability should not be a problem in an aquarium if proper aeration is provided and the tank is cleaned, and water changed regularly.
However, in open ponds, the level of dissolved oxygen in the water may fluctuate widely due to the effects of phytoplankton. If the phytoplankton blooms, as happens when there is a sudden increase in nutrients or change in temperature in the water (such as after rain on a hot day), then very high dissolved oxygen results during the day due to the production of oxygen during photosynthesis. Conversely, extremely low oxygen results just before daybreak when the oxygen required for respiration by the phytoplankton and other organisms in the water exceeds the amount of oxygen produced by photosynthesis during the day. Low dissolved oxygen in the water causes stress and affects the spawning performance of the fish.
Conversely, extremely low oxygen results just before daybreak when the oxygen required for respiration by the phytoplankton and other organisms in the water exceeds the amount of oxygen produced by photosynthesis during the day. Low dissolved oxygen in the water causes stress and affects the spawning performance of the fish.
The ammonia content of the water is another important factor that needs special attention. There are two forms of ammonia in water: ionised ammonia and free ammonia. Only free ammonia is toxic to fish, and levels of this compound should be kept within the tolerable level for the particular species which, in the case of spawning Dragon Fish, is 0.01 ppm (mg/1).
There are many water test kits available from the aquarium and pet shops to check ammonia in water. However, these tools measure only total ammonia and not the free ammonia. To ascertain the latter, you can convert the whole ammonia readings to free ammonia values if you also measure the water temperature and pH. The percentage of free ammonia within total ammonia increases with increase in water temperature and pH.
In the case of Dragon Fish that you want to breed, where water pH is maintained below 7 and ambient water temperature is below 30°C (86°F), free ammonia constitutes only1% or less of the total ammonia and, under such conditions, free ammonia should be within tolerable levels of 0.01 ppm (mg/1) if the total ammonia reading is below 1 ppm (mg/1) (that is,1% of1ppm = 0.01 ppm (mg/1)).
On the other hand, when the pH in pond water is increased to 8.5 or more, which is quite common during a phytoplankton bloom, the percentage of free ammonia increases to about 20%. At the same total ammonia of1 ppm, the free ammonia content becomes 20 times the critical level of 0.01 ppm (mg/1) (that is, 20% of1 ppm (mg/1) = 0.20 ppm (mg/1)). Hence, it is critical to prevent the occurrence of phytoplankton blooms in the spawning ponds. Otherwise, the high pH may cause ammonia toxicity and, subsequently, affect the spawning performance of the fish.
In the event of any of the above parameters not being met, it is always advisable to replace the culture water and replace it with new clean water. However, it is not necessarily true that great water replacement is better for the fish, as a water change is, in itself, a form of stress. This is because the environment is altered with a change of water, and the fish has to adapt to this sudden change in its sin-roundings. This is especially true when there is a temperature difference between the new water and culture water.
To minimize the stress suffered by the fish, check water temperatures before effecting the change to ensure minimally or no difference in both glasses of water at the time of adding the new water. Another way of achieving this is to modify the water gradually to allow the fish time to adapt.The frequency of water change could also be reduced and be dictated by the quality of the culture water.
While water which turns turbid is a good indication that it is time for a change, this, alas, could be too late, as stress to the fish may have set in by that time, affecting spawning performance. A more reliable way is to check the various water quality parameters described, that is, pH, dissolved oxygen and ammonia. Water should be changed partially when the pH falls below 6.0 or rises to about 8.0, or when total ammonia exceeds 1 ppm (mg/1).As a general guideline, it is best to change the water once every one or two weeks and change about 30-40% of the total water volume on each occasion.
Feeding plays a significant role in helping fish to spawn. Dragon Fish are hardy, and healthy adults should survive well even if they are not fed for up to six months or more. However, this would have an adverse impact on their spawning capability.
Fish used for breeding should be well fed at all times, regarding both the quality and quantity. It is best to feed the spawners a variety rather than a single type of food.This ensures that nutritional deficiency is avoided. In general, trash fish and shrimp are considered suitable food for the spawners.
You should avoid feeding the spawners with insects such as cockroaches and crickets and reptiles such as house lizards, as these may be contaminated with pesticides.
It is wrong to assume that the more food given to the fish, the better this is for them. The amount of food eaten by Dragon Fish affects not only their growth but also their gonadal development, that is, development of the testes and ovaries. Dragon Fish which are overfed develop more mesenteric fat around the gonads, and this adversely affects gonadal development, especially so in the case of testicular development in male fish. In general, the feeding rate should be maintained at less than 2% of the fish body weight per day
Male Dragon Fish mature earlier than females. Most male fish mature at 3-4 years and female fish at 4-5 years. Our experience in spawning the fish in earthen ponds shows that spawning in the population takes place throughout the year. About two to three months before spawning, the fish select their partners and form pairs, after that the couple starts to display the unique courtship behavior of Dragon Fish. Initially, the couple swims in circles, with the male trailing the female.
This behavior is easily visible in ponds at night with the assistance of a strong spotlight. About one or two weeks before spawning, the two fish swim side by side, and there is a lot of body contact between the pair. Feeding drops drastically towards the time of breeding.
Immediately after spawning, the male picks up the fertilized eggs in his mouth and broods them until the eggs hatch, and the larvae develop into free-swimming fry. In farming practice, the larvae, still with their yolk sacs, are removed from the father’s mouth approximately two weeks after spawning. Removal of the eggs is carried out during a real check for brooding males.
To release the eggs or larvae, the mouth of the brooding man is gently prised open. An average of 30-35 larvae can be found in a single brood, with the maximum recorded for Red Dragons being 62 and for Gold and Green Dragons 93 each. Research by the PPD with a Upftggj commercial farm showed that about 5-17% of the male spawners in a pond could be found brooding at a single checking operation, the average brooding rate being 12.4%.
By implanting an electronic micro tag into selected males (see page 75), PPD researchers could 11 follow the spawning performance of individual fish. In a two-year period, it was found that about 30% of the male spawners incubated eggs or larvae in their mouth at least once, with the maximum being five times. The male fish which brooded five times produced a total of 188 larvae in that period.
This is also the same fish found incubating 62 larvae in a single family! The average interval between consecutive broods ranges from four to eight months, with the shortest interval being only 80 days.
Raising the Larvae
Dragon Fish eggs are orange-red, non-adhesive and denser than water, that is, they sink. They are relatively large, with diameters ranging from 16-18mm (0.6-0.7in). The eggs can be incubated in well (but not strongly) aerated aquarium tanks. However, more commonly, farmers would rather allow a male parent to produce its eggs, and collect the larvae from its mouth later.
Once removed from the mother, the eggs or larvae are packed in polythene bags in water and rushed to the hatchery for further rearing. Each brood of eggs or larvae from one male parent should be raised separately in aquarium tanks.
Glass aquarium tanks, each measuring 90 x 45 x 45cm (36 x 18 x 18in), are used to rear the larvae so that their development can be easily monitored. Water temperature is kept around 28-30°C (82-86°F) with the use of heater-thermostats, while dissolved oxygen is maintained at about 5 ppm (mg/1) through continuous aeration of the water. Acriflavine is added to the water to heal any injuries the fish may suffer during handling.
During the first few weeks, when the larvae are still carrying large yolk sacs, they tend to crowd together at the tank bottom and remain there most of the time. They only start swimming upward periodically when the yolk sac becomes smaller, with swimming becoming more active as the yolk sac gets absorbed. Water changes are kept to the minimum at this stage.
When the larvae reach a size of 7cm (c. 3in) TL, the yolk sac is significantly reduced, and they can swim quite freely, remaining in the upper part of the water column most of the time. At this stage, the larvae start feeding on external sources of food, such as thawed bloodworm.Water change is about 10% every two to three days.
At 8-9cm (c. 3.5 in) TL, the larvae have fully absorbed their yolk sac and changed into fry. At this time they are more active during feeding and, in addition to bloodworm, also feed on small live shrimp or fish that are added into the tank. About 20% of the tank water can be changed once every two or three days during this stage.Two weeks later, the fish can be weaned over to fish or shrimp meat.
When the fry reach 15cm (6in) TL, which is the market size, they are hardier and can be transferred to outdoor tanks or ponds for raising to adults or packed for airfreighting overseas. If held in ponds, about 20-30% of the water should be changed every day.