Production of Pangasius Catfish

The pangasius catfish, Pangasianodon hypophthalmus, is an exotic fresh water fish introduced in India during mid 90’s. It is also known as iridescent shark, due to the typically attractive appearance during the juvenile stage, which has demand in the ornamental fish trade. It is a highly migratory benthopelagic riverine fish that makes long-distance migration between upstream spawning habitat and downstream feeding habitat. It is omnivorous; the early stages feed on algae, macro vegetation, zooplankton and insects while the adult also consumes fruits, crustaceans and fish.

It is a facultative air breathing fish, which can tolerate very low DO levels even to the tune of 0.1 ppm for short durations. Owing to its fast growth rate, hardy nature, good disease resistance and adaptability to high stocking density, it is considered as a potential species for intensive aquaculture and is at the third position in the freshwater aquaculture production. Pure white meat of the fish mainly sold as fillets is a major value added commodity throughout the world.

Seed Production

Broodstock management

The broodstock pond is prepared as explained for the major carps. The adult fish collected from farms are stocked in earthen ponds of 0.1-0.4 ha size at a stocking density of 5-10 t/ha. The fish are fed twice daily with a floating pelletted feed having 35% protein at a rate of 1% of the bodyweight or trash fish/ meat at a rate of 5% of the bodyweight. Three months before the breeding season, male and female fish are segregated, kept in separate ponds and provided with feed containing 1% vitamin premix. The male attains sexual maturity in the first year, whereas the female matures in 1-2 years depending on the photoperiodic cycle.

Spawning

Usually, spawning takes place during monsoon season. Sex can be distinguished by visual examination just prior to breeding season. The mature female has big, soft and distended belly with swollen and reddish pink vent, while the male has a reddish genital opening and oozes milt when the abdomen is pressed. The ripe ovum collected using catheter has yellowish colour. The mature fish are induced to spawn by injection using synthetic hormones like Wova-FH with a single dose of 2 ml/kg bodyweight for female and 1 ml/kg for male. The fish spawn as single pair or in groups. After injection, the fish are returned to the breeding pool and both sexes are dry stripped after 5-6 hours. One fish usually spawns twice in a season. The fecundity is 4-6 lakh/kg bodyweight. The fertilised egg is round, transparent, adhesive, and greenish-brown in colour. Tannin, skimmed milk powder or milk solution (7 ml milk in l-litre water) is applied to remove the stickiness of eggs. The eggs are thoroughly rinsed with clean water, measured in a graduated bucket and kept for incubation with mild aeration.

Incubation

The fertilised eggs are incubated in round-bottomed conical-shaped transparent indoor jar (25-30 litre capacity) which holds about one litre of fertilised eggs (7.5 lakh numbers) and keep the eggs in suspension with the upward flow of water. The rate of water flow is regulated to keep the eggs in suspension. Other aspects are similar to that of incubation jar for the Nile tilapia. The egg usually hatches out within 22-26 hours at 28-30⁰C and yolk sac absorption takes place within next two days.  Hatching  rate is often  40-60%.  After  72  hours  from fertilisation, the free swimming hatchlings are collected from the jar through overblown water with collection net. To avoid cannibalism, the hatchlings are transferred to nursery pond just before full yolk sac absorption. The water used for incubation is screened, filtered and re- cycled as explained for the Nile tilapia.

Nursery rearing

The earthen nursery pond of 0.1-0.4 ha size is ideal for rearing. After preparing the nursery pond as explained for the major carps, water is filled by filtering through a fine-meshed cloth followed by adding 2000 kg/ha cow dung, 300 kg/ha groundnut oil cake and 75 kg/ha superphosphate to augment the production of natural food organisms. The larvae are stocked in nursery pond at a rate of 100-125/m² just before yolk sac absorption. Any delay in transferring the hatchling to plankton enriched pond leads to mass mortality.

The free-swimming hatchling commences aggressive feeding and becomes highly cannibalistic from 72 hours of hatching. The larvae are fed 5-6 times daily with a mixed emulsion consisting of boiled egg yolk and fish/clam/shrimp meat till 14^th day. It can be replaced with powdered rice flakes and groundnut oil cake powder (1:1) in dry form. Presence of rich population of Moina in the nursery pond reduces cannibalism substantially. Up to 8 dph, its daily feed can be partially replaced with earthworm powder. The larvae are weaned on a commercial micro-pelletted feed by 14 dph and continued till 28 dph. If adequate food is not provided, cannibalism will be significant. No water exchange is required but the evaporation loss should be replenished. It attains 8 cm size by 42 dph with a survival rate of 30%.

Packing and transportation

The seeds are harvested using a seine net after reducing the water level. Utmost care is taken when the seeds are harvested as it is highly sensitive to temperature. Conditioning, packing and transportation are carried-out similar to that of the major carps. Transpotation in large open container is preferred over closed polythene bag.

Semi Intenssive Farming in Pond

Pond construction

The earthen pond of 0.05-2 ha size with a water depth of 1-2 m is ideal. The pond is covered on top with net having a mesh size of 50 mm and sides are fenced with a stiff net of 26 mm as a bio-security measure to prevent the intrusion of fish to the natural openwater bodies.

Preparation of pond

The desiltation, bund strengthening and installation of sluices are done similar to that of the major carps.The pond is drained completely, and the bottom is sun-dried so that cracks are developed, and it is tilled to expel the toxic gases. Chlorination with bleaching powder (35 ppm) is used for the removal of pathogens, predators and weed fishes. Only a nominal dose of agricultural lime (250 kg/ha) is required since the fish prefer neutral pH. Water is let-in through the water inlet covered with a fine meshed net to prevent the entry of fish and other organisms, and the water level is initially maintained at 50 cm. Cow dung @ 4,000 kg/ha or poultry droppings @ 1000 kg/ha is added to the pond 10-15 days prior to seed stocking for augmenting live feed organisms.

Stocking

After acclimatisation, uniform sized seeds of 8 cm are stocked and fed with pelletted feed at 5% of the bodyweight for a period of 2 months till they attain the size of 15-20 g. It is graded frequently, and shooters are removed to prevent cannibalism. The advanced fingerlings of 15-20 g are stocked at a density of 2-3/m² in the grow-out pond. The production of stunted seeds are also practiced by stocking them at a very high density in a separate small earthen pond and feeding at 2% of the bodyweight. It results in the production of stunted fingerlings weighing 100-150 g. When the stunted fingerlings are shifted to a large pond at normal stocking density, it grows at a faster rate.

Feeding

The fish is an omnivore which utilizes the entire column of water and accepts domestic food remains, rice bran, groundnut oil cake and formulated floating pelletted feed having 20-28% protein. For better flesh quality, it is fed with formulated pelleted feed alone. The fish is fed twice in a day during morning and evening. The daily ration during the initial days of the stocking is 6% of the bodyweight and it is gradually reduced to 1% towards the end of culture.

Care and maintenance

Fortnightly, 10-20% of the water in the pond is replaced with fresh water. Two paddle-wheel aerators of 2 hp capacity are installed per hectare of pond area to maintain water quality. Growth assessment is carried-out monthly by cast netting. Intermittent application of agricultural lime, manure and other monitoring procedures are similar to that of the major carps.

Harvesting

It attains a weight of 2 kg within 8-10 months. It is advisable to harvest large fish from 6^th month onwards. Otherwise, they may retard the growth of smaller ones. Starving the fish for 2-3 days prior to harvest improves the flesh quality. After harvest, the fish is chilled immediately. A high productivity of 30 to 50 t/ha can be expected in a crop.

Intensive Farming in Lined Pond

Pond construction

It is usually practised in small homestead pond of 80 m² lined with polythene sheet. In soil allowing seepage of water, it is usually constructed by excavating 50 cm soil from a demarcated land of 8.9 m x 8.9 m and forming a bund of 100 cm height, 180 cm base width (including 50 cm for inner slope and 100 cm for outer slope) and 30 cm top width with excavated soil around the pond to get a final depth of 150 cm. After leveling the bottom with fine sand, cushioning materials like empty sacks are placed to avoid the puncturing of the sheet by any pointed objects. Then the pond is lined with PVC coated nylon sheet of 8.4 m x 8.4 m bottom dimension and 2.4 m height with 550 gsm thickness (total weight 88 kg) with a bottom slope of 45:1. The remaining sheet after lining 1.5 m pond depth is spread on top and outer side of the bund. The inner dimension of the pond at the top will be 9.9 m x 9.9 m. Sufficient slope of 1:0.5 is given on the inner side of the bund to prevent the slipping of the polythene lining. The outer side of the bund will be provided with a slope of 1:1. The outer dimension of the pond including bund width at ground level will be 12.5x l2.5 m. Based on the local conditions, pond can also be constructed either above or below the ground level. Likewise, dimension of nylon sheet and slope of bund may vary depending on type of soil.

Rectangular shape can also be adopted for making ponds but the carrying capacity of the pond might be adversely affected due to the formation of dead zones with no water circulation and probable ammonia accumulation. Bund can also be constructed by using sacks filled with sand around the pond where there is loose soil or where sufficient land is not available for conventional construction of bund.

Lined pond above ground and Lined pond below ground

Traditionally lined pond and Polythene lined pond

At the centre of the pond, there should be a bottom drain of 5-10 cm diameter to discharge the accumulated sludge. Drain can also be provided at one side of the pond but the efficiency may be less. Sludge can also be removed by siphoning-out from the pond bottom, if it is above the ground level or by pumping-out using a submersible water pump (1/4 to 1/2 hp), if it is below the ground level. There should be an overflow pipe either separately or connected with the drainpipe, to discharge excess water caused due to rain. If the overflow pipe is connected with drainpipe, it facilitates the removal of bottom water during rain and addition of new water as the part of water exchange.

In soil with no seepage of water, lining material is not required for the pond. In this case, use of venturi pump and removal of sludge from the pond bottom may become difficult. This can be overcome by placing the drain at the opposite end of the inlet pipe, if sufficient water supply is available for frequent water exchange. It can also be tackled by using commercial/ farm made probiotics or doubling the area of the pond for the same production.The top of pond is covered with net having a mesh size of 60-80 mm to prevent the entry of predatory birds. The sides of the pond should be fenced to avoid the entry of frog, snake, tortoise etc., if the pond is constructed below the ground level. The area prone to frequent floods should never be used for lined pond construction. There should be a provision for the entry of personnel into the pond.

Preparation of pond

The pond is filled with good quality freshwater up to a height of 125 cm. Water is let-in through the water inlet covered with fine meshed net to prevent the entry of unwanted organisms. If the water is taken from an open source, it should be disinfected with bleaching powder (35 g/m3) followed by de-chlorination by aeration. Agricultural lime is applied to enhance water pH @ 75 g/m³ for pH 4.5-5.5 and 50 g/ m³ for pH 5.5-6.5. After two days of liming, dolomite or sodiumbicarbonate @ 5-10 g/m³ can be applied to enhance alkalinity of water. Inorganic fertilizers like urea @ 2-5 g/m³ and super phosphate @ 2.5 g/m³ can be applied after stabilizing pH and alkalinity to optimum level. This will be helpful for augmenting the production of live feed organisms in the pond. The pond will be ready for seed stocking within 10-14 days.

Water quality parameters

Temperature   26-30⁰C            pH   : 6.5-7.5

Transparency: 20-40 cm           DO  : >3 ppm

Alkalinity       80-140 ppm        TAN : <1 ppm

Stocking

The pond is stocked with uniform sized seeds of 8 cm size at a stocking density of 5-10/m³ after acclimatisation. The seed should be preferably transported in drums and should be disinfected by giving dip in 2 ppm KMnO₄ followed by 20 ppt salt solution for a period of 30-60 seconds each before stocking. Quarantine of seed is preferred before releasing into pond while nursery rearing of seed in hapa is not recommended. Multiple stocking must be avoided due to the cannibalistic nature of the fish particularly during early stage.

Feeding

The fish is fed with a floating pelleted feed particularly formulated for pangasius twice in a day during morning and evening. FCR will be 1.3 to 1.5, if the culture conditions are satisfactory. The requirement of protein content, feed size and daily feeding rate with respect to fish body weight is given below, which may be slightly modified at frequent interval according to the situations to the plankton production, health condition and growth rate of fish.

Feed requirement

Care and maintenance

The sludge accumulated at the centre of the pond bottom due to the movement of the water can be removed by discharging through the bottom drain at the centre, by siphoning or by pumping-out using a 1/4 hp submersible water pump. A venturi pump of about 370 W (470 l/m) is used to reduce TAN in water by continuous water circulation and aeration and it can be used daily 2 hours during initial days and even up to 12 hours during the final days.

The water in the pond is drained weekly and replenished with fresh water @ 10% for the initial days and @ 25% in the later stage. If there is water scarcity, instead of water exchange, probiotics can be used to improve water quality.

Homemade inoculum prepared by fermenting jaggery (200 g) and rice bran (800 g) with yeast powder (10 g) in a container with 10 litre water for 36-48 hours is applied to pond water of 100 m³ once in a week to accelerate the growth of natural food organisms and keep the pond environment healthy.

Agricultural lime and sodium bicarbonate can be added to raise the pH and alkalinity respectively, if needed. Use of dolomite will stabilize both pH and alkalinity. Inorganic fertilizers are added at frequent intervals of 1-4 weeks to maintain the growth of plankton and the frequency of application is adjusted in accordance with primary productivity. When the water has plenty of plankton, the application may be delayed, but it is critical not to allow the plankton abundance to fall too low before the next fertilizer application. Growth assessment is carried-out monthly by using scoop net.

Harvesting

Generally, during a culture period of 8-12 months, the fish grows to about l-1.5 kg. Starving the fish for 2-3 days prior to harvest improves the flesh quality. A high productivity of 10 kg/m³ can be expected in a crop with a survival rate of 80%. It is better to conduct the partial harvest of large sized fish from eighth month onwards to regulate the pond biomass and to realize better market price.

Source : Department of Fisheries, Government of Kerala