The mortality of the four major cichlid fishes of Urnuoseriche Lake is the subject of this paper. Mortality I as estimated by five techniques, vary amongst the cichlid fishes, viz, Tilapia carbrae, Tilapia mariac,

Tilapia zilli cend (hrornoditilapfa guntheri. The highest mortality rate was recorded for T mariac where the

total mortality (Z) was 2.06; and natural mortality (M) was 1.8949. This species was also the most highly

exploited species of fish with an exploitation ratio of0.566 (56.6%) and exploitation rate of 0.494. The least

exploited cichlid fish is (. gun/hen where an exploitation ratio of 0.43209%) and exploitation rate of 0.2225

was recorded. In C'. guntheni, total mortality was 0.726 and natural mortality was 0.413 1. In T zilli, total

mortality was 1.0547 wile exploitation ratio was 0.3674 (3 6.74%) and an exploitation rate was 0.2394. In T

cahrae. total mortality was 1.8662: exploitation ratio was 0.4786 with an exploitation rate of 0.4045. (7 page document

Anene, Afamdi

English

Aquatic Commons

MORTAUTY ESTMAT€S OF THE FOUR MAJOR CCHUD FSHES
OF UMUOSERNCHE LAKE. MO STATE, NGERA.
By
Afamdi Anene
Faculty ofAgricullure and Veterinary Medicine,
Abki State University, Umucthia Campus, U,nual,ia,
Abia State, Nigeria.
ABSTRACT.
rhe mortality of the four major cichlid fishes of Urnuoseriche Lake is the subject of this paper. MortalityI as estimated by five techniques, vary amongst the cichlid fishes, viz, Tilapia carbrae, Tilapia mariac,
Tilapia zilli cend (hrornoditilapfa guntheri. The highest mortality rate was recorded for T mariac where the
total mortality (Z) was 2.06; and natural mortality (M) was 1.8949. This species was also the most highly
exploited species of fish with an exploitation ratio of0.566 (56.6%) and exploitation rate of 0.494. The least
exploited cichlid fish is (. gun/hen where an exploitation ratio of 0.43209%) and exploitation rate of 0.2225
was recorded. In C'. guntheni, total mortality was 0.726 and natural mortality was 0.413 1. In T zilli, total
mortality was 1.0547 wile exploitation ratio was 0.3674 (3 6.74%) and an exploitation rate was 0.2394. In T
cahrae. total mortality was 1.8662: exploitation ratio was 0.4786 with an exploitation rate of 0.4045.
INTRODUCTION
The Umuoseriche man-made lake is located in the
freshwater swamps of the Niger delta floodplain
and is fed during the drains by the Udrashi River
and other smaller drivers. Of the seventeen species
of fish that inhabit the lake, cichuids are the
dominant species. constituting about 92.25% by
number and 78.15 by weight (Anene, 1998). These
stocks o fish are usually exploited by the local
people using dragnets, long set lines of various
mesh sizes, hook and line, and basket traps, without
recourse to the exploitation ratio.
The exploitation ratio is an index, which measures
whether a fishery is over fished, or not. It is based
on the theory that the optimal value of exploitation
is equal to 05. This value of exploitation ratio is one
the theory that sustainable yield is opined when the
fishing mortality co-efficient is equal to the natural
mortality (Pauly, 1983). Information on the
mortality of cichlid fishes is limited to Landau,
194
1979 that worked on lake Kinneret in Israel and
Tweddle and Turner, 1979 and as such, little is
known on the exploitation levels of fishes in this
lake as well as similar ecosystems in the Niger
delta.
This study is part of a more comprehensive
program on the ecology of cichuid fishes in
Umuoseriche man-made lake (Anene, 1996,
1998). This particular study is based on the
mortality of four major cichlid fishes in the system
with emphasis on the various ratios of
exploitation.
MATERIALS AND METHODS
The procedure used in this study was the one-man
active seining methodology provided by Wingate
and Schupp (1985), and similar to the
experimental trawl fishing technique of
Schroeder (1984). In the one-man active seining were also carried out in the open deeper waters
technique, one end of the net is fixed to the pole with
the lead line as close to the bottom as possible and
the float line on the surface of the water. The loose
end of the net is then stretched with the net in the
- same position to a distance equal to its length. It
was then volume of water and all the fish therein.
Where the loose end touches the fixed end, the net is
slowly pulled. 'I'he float line is pulled faster than
the lead line so that it rolls over to form a crib. The
operation is completed if all the net converges at the
Ii xed end and all the fish entrapped are removed.
The operation lasts for 40 to 50 minutes.
Sampling was routinely done on the first Saturday
of every month between April 1996 and March
1997. Sampling time was between 0900 hrs and
l600hrs. A gill net measuring 12m by 2 and a
stretched mesh size of 40mm was used for
sampling. During each sampling trip, four or five
random operations were made on the shallow
margins characterized by submerged and emergent
vegetation while the same number of operations
7 NK
N±1 (InL—L'
bringing the total to 8 10 operations per trip.
After few months of sampling, basket traps to
target dermesal fishes, which appeared to be rate
in the samples. Dishes caught in the basket were
no different from those caught in the seine net.
Fish samples caught were immediately opened up
and immersed in 10% formal in and transported to
the laboratory where the were identified to species
level using keys provided by Boulenger, (1909,
1916), Pellegrin, (1912); Daget, (1954), Gras,
(1'961). Blache, (1964), I)aget and Iltis, (1965),
Stanch, (1966), Thys (1966), Reed et.al. (1967),
Loiselle (1979), Leveque eLal. (1990).
Representative samples of cichlids were also sent
to the Laboratorium voor lchthyologie in
Tervuren, Belgium for confirmation of identified
samples. Samples were givemi a registration
number, weighed to the nearest 0.1 mg on a Metler
balance. Their total and standard lengths were
also measured to the nearest 1mm on a measuring
board.
(1)
\Vhere n is the number of• from which the mean length (Li) was calculated, L is the length of the longest
fish in the sample, L' is the length of the smallest fish in the sample and K is growth parameter calculated
from Von Bertalanfys growth formula(VBGF).
Natural mortality (M was calculated from Taylor's forinula(Ehrhardtet. al., 1983).
M 2.9957
T0 (2.9957)1k (2)
Where Land K are parameters ofVBGF as estimated in (Anene, 1996)
The fishing mortality co-efficient P was estimated from Pauly (1983).
F= ZM (3)
195
Where Z and M are as stated in equations 1 and 2 above.
The exploitation ration (E) was estimated from the equation (Pauly. 1983).
E F
F+M
The equation can he transformed into
E F/Z
RESULTS:
(4)
In the course of sampling, the most exploited stock
in terms of numbers was T inariae, which
contributed 36.73% and T zilhi, which contributed
25.15% of the exploited fish stack. However, in
terms of weights, T Zihli. with a percentage of
3 6.0% was more exploited than T mariae where
the percentage was 3 4.9% (Table 1). In terms of
total number of fish caught, C. guntheri (15.25%)
and T ecthrc.ie (18.52%) were riot as exploited as T
inariae and T zihli. The pattern of exploitation
was same in terms of weight.
Table 1: Percentage contribution of the major cichlid fishes to total fish catch in
ljmuoscriehe man-made Lake.
I Species Number (x lOON) % Number Weight (xlOZ)g % weight
I C. guntheri 99 15.25 4994,16 9.48
T. cabrae 120 18.25 5747.79 10.92
T. inariac 238 36.73 18382.01 34.9
T. zilli 163 25.15 18947.5 36.0
Table 2 shows that the rate of exploitation is highest forT inciriae (0.566 or 56.66% per year) and lowest for
T ,zi/hi (0.3674 or 36.74% per year). This is irrespective of the fact that the total weight of T. zilli harvested
was higher tan for any of the other three cichlid species. The exploitation ratio for IT ccthrcw and C. guniheri
arc 0.4786 (or 47.86%) and 0.4309 (43.09%) per year respectively. The rate of exploitation (u) is also
highest for T A/for/ac (0.4940 or 49.40% per annum) and lowest for C. guntheri (0.2225 or 22.25% per year).
The rate of exploitation for IT cabrae was 0.4045 or 40.45% per annum while for IT zhhhi, it was 0.2394 (or
23.94%) per annum. Those published for IT guineensis, C guntheri and IT ivfariae.
196
The rate of exploitation (u) was estimated from the equation (Landau, 1979. Gulland. 1985).
U F/Z(I ez)
Where Z and Mare as defined in equations (1) and (2) above,
Table 2: Lengths of various fish species and estimated growth paramete s (K and 'j
Species L"(nim) L (mm) K T0 (Years)
C. guntheri 88 160 0.4202
-
0.123
T. cabrae 63 178 1.1366 0.443
T.rnariae 106.0 191.0 0.7404 0.162
T. zilli 90.0 234.0 0.6888 0.141
Table 3: Estimates mortality rates in the major cichlid fishes of Umuoeriche marmade lake
Species Z M F t E
C. guntheri 0.726 0.413 1 0.3 129 0.2225 0.4309
T. cabrac 1.8662 0.973 1 0.8931 0.4045 0.4786
T. mariae 2.062 1.8949 0.1671 0.4940 0.5660
T. zilli 1.0547 0.6672 0.3875 0.2394 0.3674
(Z Total mortality, M = Natural mortality, F = Fishing mortality, E = Exploitation ratio and
p. = exploitation rate).
Total mortality co-efficient (Z) was 0.726, 1.866.2.062 and 1.054 for C gunther, T cabrae, T inariae and T
zilli respectively while the mortality co-efficient for these cichlid fishes was the most highly exploited stock
with an exploitation ratio (E) of 0.566. The least exploited stock is T zilli with a ratio (E) of 0.367. C
guntheri and T ccibrae have an exploitation ratio (E) of 0.431 and 0.479, respectively.
DISCUSSION
Even though mote T zilli were caught on weight-
weight basis, T inariae remains the most exploited
stock of cichlid fisheries resources. The rate of
exploitation is in excess of 0.5 and thus at the rate of
238 x 102 or 18382 x 102 kg per annum, this species
of fish stands the risk of being over-exploited. At a
rate of exploitation recorded for C. guntheri, T
cahrae, and T Zilli, these species of fish can be
exploited without fear ofover-fising.
I 7
Total mortality of marlue tuu i. wci
relatively higher than for the other cichlid fishes
because they preyed on by C. guntheri which itself
suffers the lowest level of mortality. Their
relatively smaller size makes tern more
susceptible •to predation than T zilli. Other
predators in the system include 1-Jepsetus odoe,
Clarias species (Anene, 1998).
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Mortality estimates of the four major Cichlid fishes of Umuoseriche Lake, Imo State, Nigeria

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Mortality estimates of the four major Cichlid fishes of Umuoseriche Lake, Imo State, Nigeria

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