Kaix
07-28-2006, 09:23 AM
The north-east region of India is a veritable paradise of freshwater fish biodiversity. In fact, in the state of Assam alone, 185 species belonging to 98 genera under 34 families have been recorded so far. Some of Assam’s fish are attractive to foreign markets as ornamental fish. One of these fish is the giant danio, which is the focus of this article. This is one of several danio species belonging to the family Cyprinidae, sub-family Danioninae, which are found in the natural waters of Assam.
Features & Habitat
The giant danio is suitable as an ornamental fish because of its attractive coloration. Its body is silvery white, its dorsal side is golden-olivaceous and its ventral side is pale in colour. A dark blue longitudinal band extends from the base of the caudal fin to the level of the dorsal fin insertion. Faint yellowish gold lines are present on either side of the central blue band. During a survey, we recorded a maximum standard length (from snout to base of the tail) of 9.50cm.
The giant danio is mostly found in the rocky torrential hill streams of India, Bangladesh, Myanmar, Nepal and Sri Lanka. For our survey, the fish were collected at maturing stage from a river stream located at Basistha, near Guwahati in Assam, between the months of January and February. The fish were caught with the help of local fishermen using cast nets and were transported to the wet lab of the College of Fisheries, Raha, Assam, in oxygen-filled polythene bags. They were found to be very hardy, compatible, fast-swimming fish exhibiting schooling behaviour. They move very fast while taking food and prefer to take feed from the upper layers of water in aquaria.
The giant danio accepts almost all kinds of food, including boiled egg, but prefers live foods, such as mosquito larvae, blood worms and tubifex worms.
Sexual Dimorphism
In natural populations, males seem to be fewer in number than females (only 30 to 40 per cent of the collected samples were found to be male). Males are slenderer, longer and more colourful, with prominent golden blue stripes, while females are comparatively deep, shorter and with faint stripes on the body. The mouth of the female is pointed. The fin edges of the males are smooth, while those of the females are coarse.
The fish attain first maturity within one year when they are about 6 to 7cm in length.
Breeding
The eggs, which are scattered by the spawning fish, are whitish-translucent in colour, about 0.9mm in diameter and somewhat semi-adhesive in nature.
The species is known to breed twice a year in its natural habitat - between April and May, and between November and December. However, in our study, we could breed the fish several times during the monsoon season (between April and August). The captive-reared fish could not be induced to breed during the winter months. However, freshly collected mature specimens from the wild may be induced to breed in captivity during November and December.
Captive Breeding Trials
A ratio of 2 males:1 female proved ideal for captive breeding purposes.
Hormones
Ovaprim and carp pituitary extract (CPE) were used in our breeding trials. CPE was found more suitable than ovaprim, as the latter caused weakness in the injected fish. CPE was prepared using five pituitary glands in 1 ml of distilled water. A suitable dose was three units to females and two units to males (1 unit = 0.025ml.). This formulation gave the best results.
The Breeding Set-up and Data
The aquaria used measured 80cm by 35cm by 35cm.
Bed: 8 to 5mm size pebbles were placed at the bottom, in a layer up to 2cm thick.
Water depth: Required water depth is 10cm, of which 60 per cent should be rainwater.
Filter: One water filter wrapped with fine-meshed cloth was used to create a mild water current.
Thermostat: The thermostat was adjusted to 27ºC.
Water quality parameters:
pH : 7.8-8.2 (pH 7.9 was found ideal)
Temperature: 27-28ºC
Dissolved Oxygen (DO): 6.5-9.0 mg/l
Total hardness: 2.5m mol/l
Ammonium: nil
Nitrate: nil
Several breeding trials were conducted, with the successful ones revealing the following important data:
Fertilisation: 80 to 90 per cent
Hatching: 75 to 83 per cent
Time for spawning: 10 to 12 hours
Time for hatching: 24 to 28 hours
Time for yolk absorption: 55 to 60 hours
Larval length (after hatching): 1.8-2.1mm
Total number of hatchlings (from one set): Range: 315 to 350
Mean survival rate of larvae: 65 to 70 per cent (on sixtieth day).
Observations:
Newly-hatched larvae usually attach themselves to the wall of the aquarium or to stones. They are transparent, like glass splinters. The longitudinal stripes of the larvae begin to develop from the thirtieth day onwards. Seventy-five units of larvae can be easily reared in an aquarium measuring 80cm by 35cm by 35cm size containing 10cm of water depth.
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The Giant Danio’s Place In India’s Ornamental Fish Industry
In India, Danio aequipinnatus (giant danio) has been recognised as an important indigenous ornamental fish of the country. In fact, the Marine Products Export Development Authority (MPEDA) has included it in its list of ornamental fish exported from India. However, precise export figures are unavailable, as the export of Indian ornamental fish falls under the nonorganised sector. Moreover, I have also learned that, over the past few years, some fish breeders from Kolkata have been to the Basistha stream in Assam to capture giant danios.
To popularise this fish in the domestic Indian market, we have conducted workshops, seminars, awareness camps and exhibitions. In addition, we have also trained 40 people, selected by the MPEDA from all the states of north-east India, in two batches, in 2004 and 2005. They were given four to five days of hands-on training on captive breeding of several species of ornamental fish. The Assam Agricultural University is, however, only able to provide transfer of technology and is not in a position to become directly involved in entrepreneurship. For this, MPEDA is now promoting a few trained individuals to become ornamental fish breeders for the local and export market. Banks have also begun providing finance for feasible captive breeding schemes of ornamental fish.
Features & Habitat
The giant danio is suitable as an ornamental fish because of its attractive coloration. Its body is silvery white, its dorsal side is golden-olivaceous and its ventral side is pale in colour. A dark blue longitudinal band extends from the base of the caudal fin to the level of the dorsal fin insertion. Faint yellowish gold lines are present on either side of the central blue band. During a survey, we recorded a maximum standard length (from snout to base of the tail) of 9.50cm.
The giant danio is mostly found in the rocky torrential hill streams of India, Bangladesh, Myanmar, Nepal and Sri Lanka. For our survey, the fish were collected at maturing stage from a river stream located at Basistha, near Guwahati in Assam, between the months of January and February. The fish were caught with the help of local fishermen using cast nets and were transported to the wet lab of the College of Fisheries, Raha, Assam, in oxygen-filled polythene bags. They were found to be very hardy, compatible, fast-swimming fish exhibiting schooling behaviour. They move very fast while taking food and prefer to take feed from the upper layers of water in aquaria.
The giant danio accepts almost all kinds of food, including boiled egg, but prefers live foods, such as mosquito larvae, blood worms and tubifex worms.
Sexual Dimorphism
In natural populations, males seem to be fewer in number than females (only 30 to 40 per cent of the collected samples were found to be male). Males are slenderer, longer and more colourful, with prominent golden blue stripes, while females are comparatively deep, shorter and with faint stripes on the body. The mouth of the female is pointed. The fin edges of the males are smooth, while those of the females are coarse.
The fish attain first maturity within one year when they are about 6 to 7cm in length.
Breeding
The eggs, which are scattered by the spawning fish, are whitish-translucent in colour, about 0.9mm in diameter and somewhat semi-adhesive in nature.
The species is known to breed twice a year in its natural habitat - between April and May, and between November and December. However, in our study, we could breed the fish several times during the monsoon season (between April and August). The captive-reared fish could not be induced to breed during the winter months. However, freshly collected mature specimens from the wild may be induced to breed in captivity during November and December.
Captive Breeding Trials
A ratio of 2 males:1 female proved ideal for captive breeding purposes.
Hormones
Ovaprim and carp pituitary extract (CPE) were used in our breeding trials. CPE was found more suitable than ovaprim, as the latter caused weakness in the injected fish. CPE was prepared using five pituitary glands in 1 ml of distilled water. A suitable dose was three units to females and two units to males (1 unit = 0.025ml.). This formulation gave the best results.
The Breeding Set-up and Data
The aquaria used measured 80cm by 35cm by 35cm.
Bed: 8 to 5mm size pebbles were placed at the bottom, in a layer up to 2cm thick.
Water depth: Required water depth is 10cm, of which 60 per cent should be rainwater.
Filter: One water filter wrapped with fine-meshed cloth was used to create a mild water current.
Thermostat: The thermostat was adjusted to 27ºC.
Water quality parameters:
pH : 7.8-8.2 (pH 7.9 was found ideal)
Temperature: 27-28ºC
Dissolved Oxygen (DO): 6.5-9.0 mg/l
Total hardness: 2.5m mol/l
Ammonium: nil
Nitrate: nil
Several breeding trials were conducted, with the successful ones revealing the following important data:
Fertilisation: 80 to 90 per cent
Hatching: 75 to 83 per cent
Time for spawning: 10 to 12 hours
Time for hatching: 24 to 28 hours
Time for yolk absorption: 55 to 60 hours
Larval length (after hatching): 1.8-2.1mm
Total number of hatchlings (from one set): Range: 315 to 350
Mean survival rate of larvae: 65 to 70 per cent (on sixtieth day).
Observations:
Newly-hatched larvae usually attach themselves to the wall of the aquarium or to stones. They are transparent, like glass splinters. The longitudinal stripes of the larvae begin to develop from the thirtieth day onwards. Seventy-five units of larvae can be easily reared in an aquarium measuring 80cm by 35cm by 35cm size containing 10cm of water depth.
--------------------------------------------------------------------------------
The Giant Danio’s Place In India’s Ornamental Fish Industry
In India, Danio aequipinnatus (giant danio) has been recognised as an important indigenous ornamental fish of the country. In fact, the Marine Products Export Development Authority (MPEDA) has included it in its list of ornamental fish exported from India. However, precise export figures are unavailable, as the export of Indian ornamental fish falls under the nonorganised sector. Moreover, I have also learned that, over the past few years, some fish breeders from Kolkata have been to the Basistha stream in Assam to capture giant danios.
To popularise this fish in the domestic Indian market, we have conducted workshops, seminars, awareness camps and exhibitions. In addition, we have also trained 40 people, selected by the MPEDA from all the states of north-east India, in two batches, in 2004 and 2005. They were given four to five days of hands-on training on captive breeding of several species of ornamental fish. The Assam Agricultural University is, however, only able to provide transfer of technology and is not in a position to become directly involved in entrepreneurship. For this, MPEDA is now promoting a few trained individuals to become ornamental fish breeders for the local and export market. Banks have also begun providing finance for feasible captive breeding schemes of ornamental fish.