8. MISCELLANEOUS

8.1. Economics
8.2. Diseases
8.3. Hybridization

8.1. Economics

8.1.1. Economics of fingerling production
8.1.2. Economics of polyculture and monoculture

Limited information is available concerning the economics of catfish rearing in Africa due to the fact that most of the work carried out to date has been oriented toward the technical development and implementation of fish rearing techniques. However, some economic information as obtained by the authors from large research stations in the Republic of the Congo (13 ha) and in the Central African Republic (3.5 ha) are presented.

8.1.1. Economics of fingerling production

In the Republic of the Congo the farm cost for the production of fingerlings in protected nursery ponds was US$ 0.07/fingerling. By contrast, the production costs for an indoor hatchery in the Central African Republic, using Artemia salina nauplii and formulated feed were US$ 0.14/fingerling. Table 15 presents an economic comparison of the two different fingerling production systems.

Table 15. Division of costs (expressed as % of the total costs) of two African catfish production systems: pond rearing and hatchery rearing using Artemia salina nauplii and formulated feeds.

	Pond rearing (% of total costs)	Indoor hatchery rearing (% of total costs)
Labour	68.0	16.2
Operating costs	25.9	27.6
Depreciation of investments (15 years)	6.1	56.2

The production of fingerlings in ponds is labour intensive, whereas indoor hatchery production is capital and technology intensive. Small-scale, privately operated fingerling production units based on nursing within protected ponds is at present the best option for fingerling production in rural Africa. Investment costs per unit with an annual production of 280 000 fingerlings was estimated to be about US$ 12 000¹³ and economically feasible with an Economic Rate of Return¹⁴ of 58%, and a net cash flow of US$ 9 500/year. (Details of the economic analysis are presented in Table 16).

¹³ 1990 price level, the Republic of the Congo
¹⁴ ERR is calculated over a 30-year period

Production parameters
Production	35 fingerlings/m2
No. of rearing cycles	8 cycles/year
Average weight/fingerling	3 g
Pond size	200 m2
Total pond area	1 000 m2
Total fingerling production	280 000 fingerlings/year
Food conversion rice bran	7
Inputs
Rice bran	5 880 kg/year
Broodstock feed	800 kg/year
Labour	30 person-months
Material	1 000 US$/year
Sundry	200 US$/year
Operation & Maintenance	10%
Prices
Rice bran	0,25 US$/kg
Brood stock feed	0,8 US$/kg
Fingerlings	0,1 US$/piece
Labour	450 US$/month
Investments		Percentage of Investments
5 ponds, 200 m2 each	6000 US$	50%
1 broodstock pond, 200 m2	900 US$	8%
Building with basins	3000 US$	25%
Store	2000 US$	17%
TOTAL	11 900 US$	100%
Farmcost/’000 piece		Percentage of Costs
Feed	7,5 US$/’000 piece	11%
Labour	48,2 US$/’000 piece	73%
Material	3,6 US$/’000 piece	5%
Sundry	0,7 US$/’000 piece	1%
O&M	6,0 US$/’000 piece	9%
TOTAL	66,0 US$/’000 piece	100%
Investments/’000 piece
Rearing ponds	21,4 US$/’000 piece
Broodstock pond	3,2 US$/’000 piece
Building	10,7 US$/’000 piece
Store	7,1 US$/’000 piece
TOTAL	42,5 US$/’000 piece

8.1.2. Economics of polyculture and monoculture

This chapter presents preliminary information on the economic performance of polyculture and monoculture operations with African catfish. However, it should be mentioned at this point that the analysis is made on the basis of biological data compiled for monoculture operations in the Central African Republic (1984-1985), and biological data compiled for polyculture operations in the Republic of the Congo (1986-1990) using prices from the Republic of the Congo (1990, US$ 1 = FCFA 285). The main economic parameters are summarized in Table 17 and details are given in Tables 18 and 19.

Table 17. Economic parameters of monoculture of C. gariepinus and polyculture of C. gariepinus with O. niloticus.

Parameters	Monoculture	Polyculture
Production (kg/ha/crop)	10 000	6 500
Investments (FCFA/400 m2)	180 000	180 000
Farm costs (FCFA/100 m2)	114 000	36 000
ERR (%)	35	56
Net Cashflow (FCFA/400 m2/year	118 000	120 000

Comparison of the data from an economic point of view indicates that polyculture is slightly more economic due to a higher Economic Rate of Return. However, the net cash flow for the farmer is more or less the same. The main difference between the culture systems is in farm costs which are much higher for monoculture because formulated feed is required so as to cover the protein requirements at the given production level.

TABLE 18: ECONOMICS OF MONOCULTURE OF CLARIAS GARIEPINUS

Production parameters
Production level	100 kg/100 m2
No. of rearing cycles	1,8 Cycles/year
Stocking density	10 fingerlings/m2
Pond size	400 m2
Food conversion composed feed	3
Total annual production	720 kg
Inputs
Fingerlings	7200 No./year
Composed feed	2160 kg/year
Fertilizers	270 kg/year
Labour	80 person-days/year
Sundry	20000 FCFA/year
Operation & Maintenance	10%
Prices
Composed feed	140 FCFA/kg
Fertilizers	80 FCFA/kg
Catfish fingerlings	10 FCFA/piece
Labour	1000 FCFA/dav
C. gariepinus (200 g)	800 FCFA/kg
Investments
1 pond (400 m2)	150000 FCFA
Equipment	30000 FCFA
TOTAL	180000 FCFA
Farmcost/100 m2		Percentage of costs
Feed	75600 FCFA/100 m2	66%
Fertilizers	5400 FCFA/100 m2	5%
Fingerlings	18000 FCFA/100 m2	16%
Sundry	5000 FCFA/100 m2	4%
O&M	10400 FCFA/100 m2	9%
TOTAL	114.400 FCFA/100 m2	100%
Investments/100 m2		Percentage of investments
Pond	37500 FCFA/100 m2	83%
Equipment	7500 FCFA/100 m2	17%
TOTAL	45 000 FCFA/100 m2	100%

TABLE 19: ECONOMICS OF POLYCULTURE OF CLARIAS GARIEPINUS WITH OREOCHROMIS NILOTICUS

Production parameters
Production level	65kg/100 m2
No. of rearing cycles	1,8 Cycles/year
Stocking density O. Niloticus	2,2 fingerlings/m2
Stocking density C. Gariepinus	0-8 fingerlings/m2
Pond size	400 m2
Food conversion rice bran	7
Total annual production	468kg
Percentage male tilapia at harvest	65%	304 kg/year
Percentage female tilapia at harvest	15%	70 kg/year
Percentage tilapia fingerlings at harvest	3%	14 kg/year
Percentage catfish at harvest	17%	80 kg/year
Inputs
Tilapia fingerlings	1584 No./year
Catfish fingerlings	576 No./year
Feed	3276 kg/year
Labour	80 person-days/year
Sundry	20000 FCFA/year
Operation & Maintenance	10%
Prices
Rice bran	30 FCFA/kg
Tilapia fingerling	6 FCFA/piece
Catfish fingerlings	10 FCFA/piece
Labour	1000 FCFA/day
Male Tilapia (200 g)	600 FCFA/kg
Female Tilapia (100 g)	250 FCFA/kg
African Catfish (200 g)	800 FCFA/kg
Investments
1 pond (400 m2)	150000 FCFA
Equipment	30000 FCFA
TOTAL	180000 FCFA
Farmcost/100 m2		Percentage of costs
Rice bran	24570 FCFA/100 m2	67%
Tilapia fingerlings	2376 FCFA/100 m2	6%
African catfish fingerlings	1440 FCFA/100 m2	4%
Sundry	5000 FCFA/100 m2	14%
O&M	3339 FCFA/100 m2	9%
TOTAL	36.725 FCFA/100 m2	100%
Investments/100 m2		Percentage of investments
Pond	37500 FCFA/100 m2	83%
Equipment	7500 FCFA/100 m2	17%
TOTAL	45000 FCFA/100 m2	100%

8.2. Diseases

In general, diseases have not been found to be a serious problem within polyculture or monoculture operations of African catfish at low stocking densities (up to 5 fish/m²). Although some fungal, parasitic and bacterial diseases can occur these will not be described here, as this has been well described in several handbooks (Amlacher, 1970 and Reichenbach-Klinke and Elkan, 1965). However, more disease problems will be encountered at higher stocking densities (over 10/m², the “Thai rearing system”), as the pond environment often quickly deteriorates. The specific disease problems encountered at high stocking densities have been well described in two handbooks produced in Thailand (Anonymous, 1981, Tonguthai et al., 1993). However, three diseases all encountered in intensive rearing systems and indoor hatcheries in Africa are described below.

“Crack head” disease is a catfish disease which has been reported from intensive pond rearing systems and hatcheries in Africa (de Graaf, 1989, Janssen, 1985c). Although the cause of this disease is still not fully understood, adverse water quality due to overfeeding and Vitamin C deficiency are believed to be the main factors causing “crack head” disease. The reported clinical symptoms have included: slightly distended abdomen due to septicaemia haemorrhage, and occasionally exophthalmia (pop-eye). This disease can be detected at an early stage, with affected fish showing a reddish lateral line on the skull, between the two air chambers, parallel to the skull plate joints. In the final stage the skull will break laterally followed by death. As soon as the external symptoms of the disease (reddish lateral line) are observed during sampling, feeding should be significantly reduced, additional vitamin C (ascorbic acid) added to the feed mixture and the pond water replaced. Generally, fish usually recover after a few weeks, after which feeding can be increased steadily little by little.

Infections by myxobacteria was found to be a major problem in a hatchery in the Central African Republic and caused heavy mortalities in a matter of several days. The major cause is bad or poor management, the fish being damaged by handling, water quality deterioration, and increased fish stress. The reported clinical symptoms include: fish remain in a vertical position or exhibit a “waddling” swimming behaviour, with white spots appearing on the skin, especially on the fins. However, proper hatchery management reduces the risk of myxobacteria and infected fish can be treated with a Furazolidone-bath at a dose of 50 ppm for one hour.

In addition, during the yolk-sac stage, larvae sometimes develop “oedema” (body swelling) ventral from the cardiac cavity which can result in heavy mortalities (up to 90%). The major cause is believed to be due to the horizontal transmission (from female broodstock) of an Aeromonas bacteria. Infected larvae can be treated with a bath of Oxytetracycline at a dose of 50 ppm. Moreoever, Oedema in yolk-sac hatchlings can be prevented by only using healthy broodstock. For example, in the Republic of the Congo where broodstock were kept in ponds, the disease never occurred, while in Ivory Coast, where the broodstock were kept indoors, there were clinical signs of “crackhead” disease, and oedema in the yolk sac larvae was endemic (de Graaf, 1989).

8.3. Hybridization

Another catfish species which has been cultivated in Africa is Heterobranchus longifilus. By contrast, in South-East Asia other catfish species are cultivated such as Clarias macrocephalus, C. batrachus, and Pangassius sutshi. In the early eighties C. gariepinus was introduced into South-East Asia and its culture has since then spread rapidly due to its higher growth rate compared with the local catfish species. However, the introduction was not a complete success as several socio-economic factors were neglected. For example, in Viet Nam consumers refused to buy C. gariepinus at a reasonable price because of its taste and relatively large head (which cannot be consumed).

Interspecific cross-breeding in fish may lead to hybrids with valuable characteristics for culture (sterility, monosex populations, heterosis for disease resistance or growth rate, etc.).

Hybridization among the Asiatic clarids have involved C. macrocephalus and C. Batrachus (Boonbrahm et al., 1977), C. batrachus or C. macrocephalus × Pangasius sutshi (Tarnchalanukit, 1986), and C. batrachus x Heteropneustes fossilis (Mukhopadathy and Dehadrai, 1987). Moreoever, in June 1988 staff from the Department of Fisheries in Thailand succeeded in artificially crossbreeding the female C. macrocephalus with male C. gariepinus. This hybrid reportedly grows faster and has more resistance to diseases than other hybrids and the hybrid is now rapidly replacing C. macrocephalus and C. batrachus in the Thai fish markets (Tonguthai et al., 1993). This hybrid has also became very popular in Viet Nam, and in Bangladesh a hybrid between P. sutshi and C. gariepinus has recently been introduced on the market (de Graaf, unpublished data).

In Africa, hybridization trials between C. gariepinus and Heterobranchus fossilis have been carried out (Hecht and Lublinkhof, 1985 and Legendre et al., 1992). Legendre et al. (1992) found that the reciprocal hybrids were viable; their survival rates being similar to those found in the maternal species. Furthermore, the growth rate of H. fossilis and their hybrids have been found to be higher than that of C. gariepinus. However, in the reciprocal hybrids, the sexual maturity of the female was only attained after 20-21 months, which is much later than for C. gariepinus (5-7 months) or for H. fossilis (12-14 months).

However, these male and female hybrids are not sterile, and viable fry can be obtained from F2 or backcross fertilization. Despite the eventual advantages from a production point of view it is the opinion of the authors that this hybrid should not be produced as the environmental risks are too high; escaping hybrids could contaminate natural fish stocks.