Okorie, P.U.

English

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SOCOECONOMC APPRASAL OF CAGE FSH CULTURE
N OGUTA KE, NGERA
BY PETER U. OKORIE
Department ofAnimai and Environmental Biology,
ltrw State University, IM.B. 2000, Owerri,
Nigeria.
(\ guta lake is one of the largest natural lakes in south-eastern Nigeria. Traditionally, its fisheries
support a large number of fill-time and part-time fishermen with their families. However, in recent
years, like most other capture fisheries in Nigeria, fish yields have either been declining or stagnating. Fish
stocks in the lake have for long been subjected to over-fishing and use of wrong fishing methods.. The paper
proposes large-scale introduction of cage fish culture in the lake as a practical means of reducing fishing
pressure on the lake as wellas providing a sustainable means of livelihood for the local population around
the lake. Limnological characteristics of lake are described to appraise the feasibility of cage culture in the
lake. Recommendations are made on the design, choice of materials, construction and management of
cages in the lake. Cost-benefit projections based on prevailing market prices are presented.
INTRODUCTION
With a surface area of over 300 ha(Ita and Balogun,
1983), Lake Oguta is the largest natural lentie
system in the Imo river basin of southeastern
Nigeria. The lake is of a rich ichthyofaunal
taxonornic composition, represented by 28 fish
families with over 91 species of teleosts. This large
diversity of fish fauna has been attributed to the
lake's close association with the major rivers in the
area (Rivers Orashi, Njaba and Awbana) and the
RiverNigerat its lower course (Nwadiaro, 1989).
Oguta lake fisheries is a substantial means of
livelihood for hundreds of full-time and part-time
fishermen and Iheir families using a wide variety of
fishing gear including gill nets, cast nets, hooks,
traps, spears and sometimes explosives. It is a
generally accepted view that yields from most
capture fisheries in Nigeria are s1:agnating (Jamu
and Ayinla, 2003). Oguta lake is not likely to be an
exception to this general trend, considering the past
(Ita and Baloguri, 1983) and present (TSPEDC,
1999) records of high population densities of
potential fishermen around the lake and the
110
corresponding high fishing pressure on the lake.
If this fishing pressure is allowed to continue, the
fish yields from the lake will go into decline (if it
has not already done so) with adverse short and
long term ecological implications.
There is a need for shift of focus from wild fish
capture to a more organized fish culture in the
lake. When compared to similar lakes in the
region, Oguta lake has received considerable
research attention. Such studies include works on
biology of fish species (Okorie, 1984; Nwadiaro
and Okorie, 1987), morphometric, physical and
chemical characteristics of lake Nwadiaro and
Umehamn, 1985) and feasibility report on the
fisheries development potential (Ita and Balogun,
1983). There is thus ample technical information
to chart the future course of development of the
lake.
Though the lake offers substantial opportunities
for fish culture in cages and enclosures, this paper
is restricted to cage culture. Cage culture is not
ABSTRAC'L
new in Nigeria. The problem is that the practice
has remained at the experimental level for over two
decades in Nigeria. There are encouraging studies
(Otubusin. 1989; Otubusin and Olatunde, 1992) on
the viability of cage culture in Nigeria, but these
scientific contributions have not yet translated to
large scale cage culture either at the subsistence or
commercial levels. In other countries of similar
socio-economic standards, cage culture has
provided spectacular opportunities for creation of
employment and large scale fish production. In
Philippines, for instance, large scale tilapia/milk
fish culture in cages is carried out in Lake Laguna
(900 km2 surface area) based on industrial and
domestic effluents of over 6 million inhabitants of
Manila. the capital city. One of the likely reasons
for the failure to popularize cage culture ii. Nigeria
is that the idea has not been properly sold to
potential farmers, especially in terms of economics
of production. This paper appraises the feasibility
and commercial viability of large scale
introduction of cages in the lake bot.h for
subsistence and comrnecial fish production.
LIMNOLOGICAL CHARACTERISTICS OF
OGUTA LAKE
Oguta Lake is located between longitude 5o42 and
5o44' east and latitude 6o45' and 6o50' north and is
situated at about 50 km north of Owerri, capital of
Tmo State. Nigeria. Fig. I shows the map of the
lake with the Njaba and Awbana rivers. The lake
empties into River Urashi. During the colonial
days the lake served as an inland port for the
evacuation of palm produce to Port-Harcourt.
Relics of landing jetties and produce wharehouses
are still present around the lake.
Oguta lake covers a maximum surface area of
about 1.80 km2 during the dry season and 2.48 km2
111
during flood season peak in October. The lake
basin is very shallow (9.30 m at the peak of flood
and 7.Om maximum in the dry season) with an
average depth of 5.5m. Two flood regimes occur
corresponding to the 'white' and 'black' floods in
July and October respectively, and the annual
drawdown is about 2Dm (Nwadiaro, 1989).
As in most humic acid rich waters of the
southern Niger delta, the conductivily is very
low (86-16.5 us cm-i), lower than that of
Lake Kainji in the north which has values in
the range 45-50 Os cm-i. This low
conductivity of Oguta lake is also reflected in the
low cation concentration and alkalinity of the
water. Apart from orthophosphates, the nutrient
ions (nitrate and silica) are generally adequate
Nwadiaro, 1989). Sodium and calcium, rather
than calcium and magnesium as in Lake Kainji
(Balogun, 1987), dominate the cations of Oguta
lake. Details of morphemetric, physical and
chemical characteristics of Oguta Lake are
shown in Table 1.
Limnological features of Oguta Lake of special
interest in cage culture include the relatively large
surface area, the low depth, substantial length of
shoreline and high dissolved oxygen content.
The lake has a surface area of over 300 ha where,
potentially, various forms of cage culture is
possible. The lakes shallowness is also an
advantage. Furthermore, the lake has a shoreline
of 10.63 km length thus offering considerable
opportunities for installation of cheaper standing
cages. In view of the high stocking rates in cages,
dissolved oxygen content is a critical
consideration for cage culture. Oguta lake is, on
the average, adequately oxygenated all year
round (range in percentage saturation. 42-)
87%) and throughout the water column. During
most of the year water flow is noticeable on the
surface and bottom, with current velocities of up to
144 cm 5-1 on the surface and 91 crn51 on the
bottom (Nwadiaro, 1989). Thus there is constant
mixing and oxygenation of lake water.
FISHING PRESSURE ON OGUTA LAKE
Based on an estimated (Ita and Balogun, 1983)
mean standing crop of 41.5 kg/ha, the total standing
crop for the 300 ha surface could be approximated
at 12.5 metric tonnes of fish. Assuming yield to be
one third of the standing crop, the expected yield is
about 4.3 metric tonnes. Interestingly, a similar
yield is obtained when the estimates are based on
Ryder (1965) morpho-edaphic index (MEl) i.e.
total dissolved solid (or conductivity) divided by
mean depth. Estimates based on MEl give a yield
of 15 kg/ha and a total yield of 14.5 metric tonnes
per annum.
Based on a standing crop of 12.5 metric tones in the
lake, if the fisheries were to be exploited optimally,
the lake should cater for only 6 full-time fishermen.
But Ita and Balogun (1983) showed that a total of
2,657 people were engaged in fishing activities on
the lake, of which 2,403 (90.4%) were full-time
fishermen while the remaining 154 (9.6%) were
either assistant fishermen or part-time fishermen
(Table 2). Table 3 is a list of fishing gear used on
the lake showing that the commonest fishing gear
was the gill net. Use of explosives was only noted
in one village.
Though this fishing survey was done long ago, it is
unlikely that the fishing pressure has lessened now
ISPEDC (1999) report showed a population of over
106,000 people in Oguta LQ.A.,. the immediate
environment of the lake. The main occupation of
the rural community is farming and fishing while a
small percentage, is involved in petty trading and
canpe transport on the lake. The grpwing human
population will thus likely reflect on an increasing
112
number of potential fishermen trying to make a
livelihood out of the lake
ECONOMICS OF CAGE CULTURE IN
OGUTA LAKE
Cages for fish culture can have a wide variety of
designs, sizes and choice of materials. Cages
may be designed to stand on the water bottom or
float, with cage sizes ranging from 1-100 rn3.
Walls of cages may he made with bamboo, sieve
cloth, nylon or metal nets. Flotation of cages
may be achieved in the old fashioned way using
eirnpty old drums while modern installations are
kept afloat using styrofoam floats.
The economic analysis in this study is based on
use of simple I m3 standing cages of 1.0 m x
1 .Orn x 1 .25m dimensions. The frames are made
of wood while nylon nets were used for the walls.
A complex of ten (10) of such cages was
considered a minimum economic unit. The
choice of standing cages in this study is largely
influenced by the long shoreline of the lake with
its relatively shallow bays. Potentially, the
approximately 10.63km shoreline of the lake can
accommodate thousands of standing cages along
its shoreline. Ideally, large complexes of floating
cages are preferred for easier management in
large-scale commercial cage culture. The
constraint of using such floating cages for
subsistence farmers is the extra cost of installing
the floats. Preliminary observations in this study
showed that installation of floats and access
wooden platforms can raise the cost of cage
construction by 50-150%.
The fish species of choice in this study is the
catfish, Clarias gariepinus, because of its
hardiness, adaptability of feeding habits, good
growth characteristics, high market value, and
availability of its fingerlings within the project
area.
Two crops of 20-30 kg fishlm3 each are possible in
cages using high quality artificial feeds. However,
use of such feeds is highly capital intensive and
could constitute up to 40-60% of the total operating
cost in intensive aquaculture (Coche, 1979). This
study assumes a production of one crop of 20
kg/m3/yr based on use of such locally available and
cheap agricultural wastes as palm kernel cakes,
groundnut cakes, brewery waste, rice bran, maize
bran and blood meal to feed the fish. Another basic
assumption in the study is the use of a 5 years life
span for the cages. Generally, the life span of nylon
cages is 3-5 years. The upper limit of 5 years life
span can be ensured by cleaning the cages regularly
and avoiding direct exposure to sunlight.
CONCLUSiON
A yearly net profit of over N3 ,200.00 (USD 24.00)
per cubic metre of cage culture is an attractive
business enterprise, higher in economic returns
than any other agricultural activity within the study
area, and highly significant in a country where GNP
per capita income is below USD 300.00. Cage
culture in Oguta lake has the potential to contribute
to rural incomes, generation of employment and
fish production. The system is particularly suited to
the rural poor who do not have access to land for any
other form of agricultural production.
From the ecological perspective, it is obvious that
cage culture will achieve a more efficient utilization
of the lake than continued over-fishing of an already
depleted fish stock in the lake. For instance, the
estimated maximum sustainable yield (MSY) of 4.5
metric tonnes in the lake is equivalent to the fish
output of just 225 m3 of intensive cage culture.
Potentially, a total fish production of about 600
metric tonnes in the lake if as much as 1% (3 ha) of
113
Table 4 shows the capital and operating costs for
ten (10) units of I rn3 cages in year 1 while Table
5 presents the cash flow projections for five (5)
years. Daily management procedure such as
feeding fish and cleaning cages is not time
consuming and cin be accommodated within
normal household activities on part-time basis.
Thus, apart fim labour costs of constructing
cages, no other provisions have been made in this
study for labour costs. Except fOr initial
operating loss in year I as a result of high capital
investment, other years (ii-v) show encouraging
profit margins (Table 5). In year 11, for instance,
there is a net profit ofN32050.00 tbr the ten (10)
cages. This translates to a net profit of
N3,205.00 (USD 24.00) for 1m3 of cage culture
inayear.
the lake is placed under intensive cage culture.
To ensure a large-scale adoption of cage culture
and enhance its economic sustainability in the
lake, government can play the following roles:
a) Re-invigoration of Oguta indoor
hatchery: Cage culture requires high stocking
rates of fingerlings. Stocking of cages in just 1%
of the surface area of the lake will require a
minimum of 1.5 million fingerlings yearly. The
government-owned indoor hatchery in Oguta
needs to be reinvigorated to meet the expected
high demand for fish fingerlings. While interest
has focused on production of Clarias and
Heterobranchus fingerlins, there is need also to
produce planktivorous species like Sarotherodon
galilaeus which can give good yields in
wastewater, with or without supplementary
feeding.
b) Rehabilitation of Njaba river: The
major inflowing river to Oguta Lake
is Njaba river. This river is now at an
advanced stage of siltation which is
having adverse hydrological influence
on Oguta lake. With time, the lake will
progressively get shallower and
smaller. There is urgent need to disilt
Njaba river and stop all forms of
deforestation within at least 50 m of its
banks.
c) Extension Services: There is need fOr
an aggressive extension effort to
dsseininate information on
establishment, management and
profitability of cage culture.
approxrniae posluon UI me taKe
114
0 0.5 LOkm
Table 1: Morphometric, physical and chemical characteristics of Oguta lake.
Characteristics Values
Morphometric & Physical
Total surface area 1.796 km 2
Maximum Length 3.0 km
Maximum breadth 0.75 km
Mean breadth 0.60 km
Maximum depth 8.0 m
Average depth 5.5 m
Relative depth 0.27 in
Length of shoreline 10.63 km
Shoreline development 1.14
Temperature 26.0-31°C
Secchi disc transparency 0.61-4.50 m
Chemical
Phosphate — phosphorus (total) 0.01-0.68 mg
Nitrate-nitrogen 0.17-2.24 mg
Silica, SãO2 2.76-26.76 mg F1
Conductivity 8.6-16.5 is cm
Dissolved oxygen (surface) 3.40-6.95 mg F'
Biochemical oxygen demand 0.11-2.60
pH 5,1-6.4
Total alkalinity (ppm CaCO3) 7.5-25.0
(Source: Nwadiaro and Urneliam, 1985).
115
Table 2. Census of fishermen on Oguta lake
No of Owner Assistant
Villages fishermen fishermen
Part-time Total
fishermen
52 2,403 167 87 2,657
(adapted from Ita and Balogun, 1983)..
Table 3: Distribution of fishing gear in 52 villages on Oguta lake
Fishing gear Distribution (%)
Gill net
Cast net
Hooks
Traps
Spear
Spear
Dynamite
Floating nets
96.2
69.2
84.6
65.4
9.6
9.6
1.9
7.7
(adapted from Ita and Balogun, 1983).
Table 4 Capital and operating costs for 10 x 1m3 cage culture for year 1.
Sub-head Material Cost (N)
Capital costs Wood 11,160.00
Nylon mesh (25.4 mm) 13,200.00
Nails etc. 1,400.00
Labour (80 man hrs 15,000.00
@ N1500.00/man hr
Sub-total 40,760.00
Operating costs Fingerlings (stocked at 6,000.00
50 fishlm3 @ N12.00/fish).
Feeding 22,500.00
Repairs 1,000.00
Sub-total 29,500.00
Grand total 70,260.00
116
Table 5: Cash Flow Projections for 10 x 1m3 cage culture for five (5) years
Years
1 2 3 4 5
=N
Capital costs 40,760 - -
Operating costs
a) Fingerlings 6,000 6,300 6,620 6,950 7,300
b) Feeding 22,500 23,600 24,800 26,050 27,350
c) Repairs 1,000 1,050 1,100 1,160 1,210
Sub-total 29,500 30,950 32,520 34,160 35,860
Grand total
expenditure 70,260 30,950 32,520 34,160 35,860
Fish price index
Clarias 3O0O0/kg 315.00 330.00 350.00 365.00
Gross income
from sales 60,000.00 63,000 66,000 70,000 73,000
Profit/(loss). (10,260) 32,050 33,480 35,840 37,140
117
REFERENCES
Coche. A.G (1979). A review of cage fish culture and its application in
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Surrey. Pp 428-441.
iS PEDC (1999). Inio State of Nigeria, projected population by localities.
Irno State Planning and Economic Development Commission, Owerri, 87 pp.
Ita. ED. and J,K. Balogun (1983). A feasibility report of the fisheries
development potentials of Oguta lake. Kainj i Lake Research Institute, New Bussa. 49 pp.
Jamu, D,M. and A.O. Ayinla (2003). Potential for the development of
aquaculture inAfrica. Naga, vol.26(3): 9-13.
Nwadiaro, C. S. (1989) Ichthyofauna of Lake Oguta, a shallow lake in
southeastern Nigeria. Arch. 1-lydrobiol 113(3): 463-475.
Nwadiaro. C. S. and P.U. Okorie (1987). Feeding habits oftheAfrican
bagrid, Chrysichthys filamentosus in aNigerian Lake. Jap. Ichtyyol. 33: 376-393.
Okorie, P.U. (1984). Same aspects of the biology ofChnysichthys
filamentosus (BOULENGER 1912) (Pisces: Bagridae) in Oguta Lake, Nigeria. M.Sc. thesis, Univ.
ofPort-Harcourt.
Otubusin, S.0. (1989). Fish culture in cages pens and enclosures: A
possibility of meeting the fish demand in Nigeria In Proceedings of the Fisheries Society of Nigeria
Conference 1989, A.D. Onyia and G.N. Asala (eds) pp 9-15.
Otubusin, S .0. and A.A. Olatunde. (1992). Utilization of waste waters in
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118



Socio-economic appraisal of cage fish culture in Oguta Lake, Nigeria

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Socio-economic appraisal of cage fish culture in Oguta Lake, Nigeria

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