AQUACULTURE SYSTEMS
Successful hatcheries are very profitable. The success rates of hatcheries vary enormously, ranging from 5 to 200 eggs to grow one juvenile. Indoor recirculation systems (RAS) are widely used in Europe (especially the Netherlands) to culture African catfish, although other systems also exist such as ponds or flow-through. The basic principles of RAS include removal of solid particles, spilled feed, dissolved organic matter and CO2, conversion of ammonium into the less harmful nitrate (nitrification) or conversion of nitrate into N2 gas (denitrification). The general design features and a schematic overview of RAS are illustrated in Figures 1 and 2, respectively.
The use of RAS in hatcheries, however, has both advantages and disadvantages. The advantages of RAS include better control of environment and diseases. Feeding efficiency of RAS is high. There is no predation. It is also easy to grade, take care and harvest the fish. RAS needs
Figure 1: General design features of RAS Figure 2: Schematic overview of RAS
1 2 3 H 4 5 1 Fish tank 2 Sedimentation tank 3 Pumptank 4 Biotower 5 Reception tank H Heater Pump Water Energy Fish tank Feed Air O2 CO2 Sedimentation tank Waste water Biofilter Pump tank Dentrification NO2 N2 (g) Nitrification NH4 NO2 NO3
limited space for installation. A bore hole is used as the only water source. On the other hand, RAS also requires intensive capital investment, high-quality infrastructure, and high running costs and feed quality.
Overall, the sections in a hatchery, based on RAS, are designed specifically for broodstock, incubation, and advanced fry and juvenile. The specific life stages of African catfish in RAS are shown in Table 1.
Technical specifications (e.g., system, tank material and size) and management parameters (e.g., stocking density, feeding, light regime, production cycle and water source) required for broodstock, incubation, and advanced fry and juvenile are respectively given in Tables 2, 3, 4 and 5. Feeds and feeding are critical factors for profitable farming of African catfish based on RAS. Different types of feeds are required for larvae, advanced fry, juvenile
Table 1: Feed and water quality parameters required for different rearing stages of African catfish Growth Age Optimal water quality parameters phase (weeks) Weight System Feed NH4 NO2 pH Temp. (oC)
Fry – larvae 0–2 0.05–0.1 g Incubation Dry diet
system 0.2–0.3 mm <3 <1 7 28
Fingerling 3–5 0.1–1.0 g Advanced Dry diet
fry system 0.3–0.8 mm <4 <2 7 28
Juvenile 5–8 1.0–8 g Juvenile Dry diet
culture system 0.8–1.5 mm <10 <2 7 28
Broodstock >–1,5 > 4 kg Broodstock Broodstock
year system diet 9 mm <20 <3 7 25
Table 2: Broodstock
System RAS or flow-through – continuous
Tank material Concrete, glass fiber or plastic Tank size 1,200–5,000 l
Stocking density Maximum of 75 kg/m3
Production cycle 180–1,500 days
Feeding regime Ad lib – less than 0.5% BW/day Light regime 12 L –12 D
Water source Bore hole
Mode of cleaning Draining components of system Number of 25 pairs
broodstock for 1 million fry
Table 3: Incubation
System RAS – all in,
all out
Tank material Plastic or glass Tank size 100–1,000 l
Stocking density Maximum of 600 g/m3
Production cycle 0–14 days Survival 40%
Feeding regime 10–8% BW/day
Light regime 0–3 days 24 L; 4–14 days low light intensity
Water source Bore hole
Mode of cleaning Disinfection of all components of system between each cycle
Table 4: Advanced fry
System RAS – all in,
all out
Tank material Plastic or glass Tank size 600–1,000 l
Stocking density Maximum of 10,000 pc/m3
Production cycle 14–40 days Survival rate 58% Feeding regime 8–6% BW/day Light regime Low light intensity Water source Bore hole
Mode of cleaning Disinfection of all components of system between each cycle
Table 5: Juvenile
System RAS or green water tank/pond system – all in, all out
Tank material Plastic, glass fiber or concrete Tank size 600–5,000 l
Stocking density RAS: maximum of 6,000 pc/m3
Green water: maximum of 400 pc/m3
Production cycle 40–61 days Survival rate 75% Feeding regime 6–5% BW/day Light regime Low light intensity Water source Bore hole or open water Mode of cleaning Cleaning of all components of
and brooders. With high-quality extruded feed, the fish can perform fast growth, low food conversion ratio (FCR), high survival rate and low deformities. The economics of fry, advanced fry and juvenile feeding is given in Table 6, which indicates that buying good quality feed is not expensive.
Grading during early stages of rearing is essential for African catfish because this is a carnivorous species displaying cannibalism from the fry stage. Cannibalism is the main cause of high mortality in hatcheries. Suboptimal (or poor) rearing conditions also induce development of shooters. Grading should be carried out once or twice during advanced fry stage and once during juvenile stage.
Another issue with RAS is maintenance and management. Without proper maintenance, problems can arise gradually in initial stages and can become serious later. For technical aspects, it is necessary to monitor water parameters regularly by periodic flushing, cleaning and disinfection. There should be a pest control program, maintenance of infrastructure, repair of farm equipment,
presence of spare parts, cleaning of environment and proper record keeping of the whole production process.
DISEASES
Diseases are related to rearing environments and management practices. Curing with medicine is a symptomatic solution only. The cause of any disease should be identified at the farm level. Threats for African catfish include toxins (CO2, NO2, NH4, chemicals), element deficiencies, overfeeding, parasites, bacteria and viruses. When the fish suffer from toxins, they show signs of hanging, brown blood, quick mass mortality, increase or decrease of slime and nervous behavior. Treatment in these cases includes flushing, salt application and ventilation. Generally, farmers don’t pay good attention to deficiencies in vitamin, minerals, fatty or amino acids. In severe cases, the fish can stop feeding and growing or can show sluggish behavior and deformities (e.g., broken heads). Immediate reaction includes feed improvement and better feed storage.
Table 6: Economics of fry, advanced fry and juvenile feeding Fry Production 100,000 fry of 0.1 g
FCR 0.6 Survival 40%
Feed Quantity *Price/kg Total
Artemia 2 kg € 55 € 110 0.2–0.3 mm dry feed 7.2 kg € 20 € 144
Total € 254 Price per fry € 0.003
Advanced Production 100,000 advanced fry of 1 g fry FCR 0.6 Survival 58%
Feed Quantity Price/kg Total
0.3–0.5 mm and 65 kg € 4 € 260 0.5–0.8 mm dry feed
Total € 260 ` Price per
advanced fry € 0.003
Juvenile Production 100,000 juveniles of 8.0 g
FCR 0.7 Survival 75%
Feed Quantity Price/kg Total
0.8–1.2 mm and 550 kg € 3 € 1.650 1.2–1.5 mm dry feed
Total € 1.650 Price per
juvenile € 0.02 * Prices are indicative only and based on 2007 data; €1.0 equivalent to US$1.33 January 2007;
Overfeeding is not recommended because the digestive system of the fish cannot cope with the feeding level or method. Typical symptoms of overfed fish include open bellies, sluggish behavior, hanging or mortality. For parasites, there are gill and skin worms or flagellates. The fish show abnormal signs such as cotton-like spots on body, inactive or sluggish behavior, increase of slime and nervous behavior. Under these situations, salt treatment and increase of water temperature are needed. There are two main bacterial diseases: aeromonas and citrobacter-related origins. The fish show symptoms such as ulcers on skin, necrosis of barbles, inactive feeding, sluggish behavior, hanging, and limited to severe mortality. They should be treated using antibiotics along with sterilization of the environment and improvement of management practices. By far, virus-related diseases are not reported in African catfish. It is wise to observe the fish closely and immediately identify abnormal behavior. Problems always have multiple causes. To distinguish the primary cause and its solution is not easy. A good farmer should identify problems before they occur.