Eiriksson, G.M.

Kaunda, E.

Likongwe, J.S.

Rwaributware, D.T.

English

Aquatic Commons

Nov 2003
66 Point of No Return" for starved larvae of the redbreasted ti1apia,Tilapi rendalli
(Boulenger9 1915)
Donat T. Rwaributware, Guôni Magnñs EirIksson, Emmanue' Kaunda, & Jeremiah S Likongwe
Department ofAquaculture and Fisheries Science, Bunda College, University ofMalawi, P.O. Box 219, Lilongwe, Malawi.
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Introduction
Tilapia rendalli (Boulenger, 1915), the red-breasted
tilapia also known as the Congo tilapia (Teichert-
coddington et al., 1997) and locally known as:
"Chilunguni" and "Nyungwesali" in Malawi, is one
of the four most widely cultured species in sub-
Saharan Africa (Penman and McAndrew 2000). In
Malawi, Tilapia rendalli comes next in importance to
Oreochromis shiranus with which it is often stocked
in polyculture in ponds. Both species are highly val-
ued as a food source (Msiska, 1988, Mandeng 1988-
cited by Kaunda 1996; Ambali, 1998, Coward and
Bromage, 2000) but T. rendalli has a reportedly supe-
rior flavour. In addition, T. rendalli performs better at
higher (and cooler) altitudes (around 1,000 m; 22 ° C)
than any Oreochroinis species available in Malawi
and may therefore be suitable for aquaculture in the
high-altitude areas where fish supply is limited
(Msiska, 1988). However, inadequate supply of fin-
gerlings is one of the constraints to fish farming in
high altitude areas as T. rendalli breeds only when
temperatures exceed 27 °C (Ohashi et al., 2001), and
the asynchronous nature of tilapia species makes it
difficult for large numbers of uniform-size fry to be
obtained naturally (Tave, 1993).
Seed production for tilapia by synchronized mas-
sive spawning in concrete tanks and hapa hatchery
systems appears to be more efficient than production
30
in ponds (Guerrero and Villanueva 1978 cited by
Antonio et al., 1988) due to elimination of preda-
tors, improved harvest efficiency and better water
quality.
However, in order to further develop massive
seed production and nursing techniques in aquacul-
ture, the understanding of biological aspects such
as effects of environmental variables on reproduc-
tive processes and morphological development vis-
à-vis feeding performance in larval and juvenile
stages, is indispensable. A typical teleost embryo
feeds endogenously on yolk reserves, but sometime
after hatching the larva takes exogenous food usu-
ally in form of microscopic plankton. Endogenous
feeding ceases as the yolk gets completely re-
sorbed, making exogenous feeding a compulsory
means to survival.
The time when fish larvae switch from endoge-
nous feeding to exogenous feeding is a vulnerable
period in the life cycle of fish and is of important
significance in the captive spawning of fish. A
common constraint to captive spawning is the lack
of food, which often occurs at around this time. It
is indeed believed that lack of suitable food is the
main cause of fry mortality (Woynarovich and
Horváth, 1980).
The point of no return (PNR) a concept first put
forward by Blaxter and Hempel in 1963 (cited by
992) is the point in time, after final yolk re-
Aqerrs-F1513 TeS Rep. Issue No: Z Nov 2003
sorption. when starved larvae lose their feeding abil-
ity, approach neutral buoyancy and become so inac-
tive tbat supply of food afterwards neither arrests
mortality nor restores normal growth and develop-
ment since the larvae would already be too weak to
eat. PNR for a species may therefore be defined as
the duration in days, of delayed first feeding, which
causes irreversible effect that larvae cannot recover
from. The PNIR for T. rendalli has not been deter-
mined and this study was conducted to establish thc
PNR in larvae of T. rendalli.
Methodology
From a single batch of eggs that hatched on 6thi Feb-
mary 2003 at 08:00 hours, two sets of experiments
each having 650 larvae were carried out. In each ex-
periment larvae were stocked in groups of 50 in 13
beakers. Treatments were in form of 12 different tim-
ings of Grst diet supply that is, feeding delayed for up
to5,6,7,8,9, 10, II, 12, 13, 14, l5,andl6daysaf-
ter hatching. The group of 50 larvae reared in the 13°
beaker were not fed. Due to shortage of uniform-size
beakers, one experiment was done using 3-litre beak-
ers and the other one in 2-litre beakers. Feed con-
sisted of Anemia nauplii except occasionary, when
due to shortage of Anemia, larvae were fed zooplank-
toil (mainly rotifers) harvested from outdoor concrete
tanks. Fish were fed 5 Anemia /zooplankton per ml
of water three times a day. To prevent deterioration of
water quality, uncaten feed from the previous day's
meals was regularly removed by siphoning, before
adding feed for each new morning. Mortalities were
recorded twice everyday until 3 days after all larvae
in the "unfed" groups were starved to death. This was
on day 20 after hatching.
Results and Discussion
By the end of 20 days, survival was more than 50%
and 30% in beakers where larvae were fed at 7 DAFT
(7 days after hatching) and 10 DAFT, respectively. For
larvae that were first fed 11-12 days after batching,
survival was below 30% in the larger beakers and
below 20% in the smaller beakers. Survival for larvae
first fed 13 days after hatching was over 5% in the
large beaker and 0% in the small beaker.
The effect of delayed feeding was greater at 13
DAH ( 300 ITAFI) between larvae fed at 8 DAH and
those not fed by then (Figure 1). The point of no re-
turn was around 13 l)AH and 14 DAFT (for the small
beakers and larger beakers respectively) (Figures 1 a
and b). Mortality due to starvation was generally
higher in smaller beakers than in the larger beakers
although the difference was not significant.
31
The PNR of 11 rendalli obtained in this study
makes sense as it is lower than the one reported for
0. inossambicus. In general, eggs of Tilapia are
smaller than those of Oreochromis species. Balarin
and Hatton (1979) and Rana (1985) established
that DAH is higher in larvae obtained from larger
than small eggs. PNR for 0. mossambicus were 15-
16 DAH and 21 DAH in larvae from small to me-
dium and large eggs, respectively (Rana 1985).
In conclusion, this study established that the point
of no return for unfed T rendalli larvae is 13—14
DAH and that delayed feeding beyond 8 DAH has
a negative impact on their survival.
Acknowledgements
The authors are grateful to Mr. B.P. Kataya, the
Hatchery and Water Quality Technician and to Mr
0. Matambo, the Officer in Charge of the Fish
Farm, Department of Aquaculture and Fisheries
Science, Bunda College of Agriculture, University
of Malawi, for their co-operation during hatchery
work. Finally, this study was conducted with finan-
cial support front the Icelandic International Devel-
opment Agency (ICEIDA) in Malawi and bene-
fited greatly from the logistical support of the Ja-
pan International Co-operation Agency ( JICA) to
the College Fish Farm.
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a)
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Issue No: 2, Nov2003
Days after hatching
b)
Figure 1. Number of surviving embryos/larvae at different days after hatching (DAH) of T.
rendalli : a) larger beakers; below, b) smaller beakers, (only selected treatments are shown)
32
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"Point of No Return" for starved larvae of the redbreasted tilapia, Tilapia rendalli (Boulenger, 1915)

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"Point of No Return" for starved larvae of the redbreasted tilapia, Tilapia rendalli (Boulenger, 1915)

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