Caridina nilotica (Roux) (Decapoda: Atyidae) was investigated over a period of four months in three zones of Lake Victoria. Abundances were estimated by vertical net sampling. The importance of C. nilotica in the diet of the three commercial fish species was investigated. Caridina nilotica is a primary food for Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin). A quantitative study of C. nilotica in the fishing area indicated high biomass which can support the Lake Victoria fisheries

Budeba, Y.L.

Aquatic Commons

The role of Garidina nilotica (Roux) hi the Lake Vici
reference to Lates niloticus (L)
155
I ra fisheries with
Y.L. BUDEBA Tanzania Fisheries Research Institute, P.O. Box 475 Mwanza, Tanzania
Abstract: Caridina nilotica (Roux) (Decapoda: Atyidae) was investigated over a period of
four months in three zones of Lake Victoria. Abundances were estimated by vertical net
sampling. The importance of C. nilotica. in the diet of the three commercial fish species was
investigated. Caridinci nilotica is a primary food for Lates niloticus (L.), Oreochroinis
niloticus (L.) and Rastrineobola argentea (Pellegrin). A quantitative study of C. nilotica in
the fishing areas indicated high biomass which can support the Lake Victoria fisheries.
Introduction
C'aridina nilotica (Roux) is an atyid shrimp typically found in benthic habitats and amongst
aquatic weeds; it grows to a length of about 25 mm TL. Car/dma. nilotica feeds on bottom
debris (Fryer 1960) and is distributed in the tropical and subtropical zones of eastern and
southern Africa. In Lake Victoria, C. nilotica occurs throughout the lake and is extremely
abundant in the littoral region wherever there are weed beds. Fryer (1960) observed two
species C. nilotica and C. africana and two forms of C. nilotica in Lake Victoria, one in the
vegetation in the littoral waters and another with an epihenthic distribution in the sublittoral
and deep waters.
Following the introduction of the Nile perch, Lates niloticus (L.), in the i950s, dramatic
changes in the Lake Victoria environment have occurred. The disappearance of
haplochromines in the 1980s was coupled with a shift in the diet of Nile perch towards C.
nilotica, Rastrineobola argentea (Pellegrin) and juvenile L. niloricus (Hughes 1986; Ogari &
Dadzie 1988; Ligtvoet & Mkumbo 1990; Ogutu-Ohwayo 1990). The rapid depletion of the
main prey items (haplochromines) did not induce a corresponding decrease in the predator
population because L. niloticus opportunistically switched to R. argentea and C. nilotica.
Stocks of these two species appear to have greatly contributed to the maintenance of the
predator population and its high catch rates.
In the early 1980s, only a few shrimps were occasionally observed iii the bottom trawl
catches in Mwanza Gulf, but after 1986 trawl catches for fish frequently contained thousands
of shrimps (Witte et a.i. 1992). In February 1992, a small trawl (cod end 5 mm) shot for 10
minutes recorded about 100 000 individuals of C. nilotica. Tweddle & Bassa(1999) recorded
40 kg of C. n/lot/ca in a 30 minutes frame trawl. Othina and Osewe-Odera (unpublished
data) reported 3180 t of C. nilotica were landed in the Kenya waters of Lake Victoria in
1995. This was 1.84% of the total landings. The reason for this increase is probably that the
predation pressure on juvenile shrimps has diminished.
The formerly abundant haplochromines were potentially predators of juvenile shrimps where
and whenever they became available. Their demise has relieved predation pressure on the
juveniles of C. nilotica. The current potential predators, i.e. small L. niloticus, however,
mainly live inshore and are not abundant throughout the year (Katunzi unpublished data).
The commercial fisheries of Lake Victoria consist mainly of piscivorous L. niloticus,
algivorous Oreochromis niloticus (L.) and zooplanktivorous R. argentea.
Caridina nilotica consume the equivalent of 2.2% of annual lake primary production. Present
net annual secondary production by the shrimp is estimated to be an order of magnitude
greater than the present fishery yield of the lake (Ignatow et al. 1996). However, the
demographic status and absolute stock size of C, nilotica, and its role in the food web of the
lake is unknown. Thus it is important to determine the shrimp biomass available to L.
niloticus, and the population biology (biomass, growth, mortality, recruitment, reproduction)
and distribution of C. nilotica.
The feeding habits of important fish species is also needed to understand the dynamics of the
fishery and lake ecosystem as a whole. Recent studies have shown juvenile L. niloticus,
haplochromines, R. argentea, C. nilotica and Odonata were the main 'food items of L.
niloticus in order of importance in both the Speke and Mwanza gulfs (TAFIRI 1996). There
is also evidence that L. niloticus exhibits ontogenic shifts in diet (Mkumbo& Ezekiel 1999)
and spatial variation in foods eaten (Owili 1999); all aspects that need further study if the role
of C. niloticus is to be elucidated.
The main objectives of this study are to improve our understanding of the population biology
of C. nilotica in relation to limnological factors of Lake Victoria and the role of the shrimp in
the food web.
The specific objectives are:
to determine the spatial and temporal distribution and abundance of C. nilotica, and relate
these to key environmental parameters.
o to study the population dynamics of C. nilotica (growth rates, mortality rates)
o to determine the importance of C. niiotica to the diet of the major commercial fish species
Material and methods
('andina nilotica were sampled daily with a vertical net with a metal frame of 1 rn x i ni
mouth opening to elucidate the temporal and spatial distribution in the three zones of the
Tanzanian sector of Lake Victoria used for the trawl survey (Mkumbo & Ezekiel 1999). It
was planned to take several samples at each station and, if possible, at different depths.
However this was not possible because of logistical problems. Other sampling techniques
such as lift net and a 'frame (box) trawl net will be used in the future, especially in deep
waters around the thermocline.
From this regular sampling programme on C. nilotica, data will be collected on abundance,
standing stock, length-frequency distribution (and consequently growth and mortality rates),
sex ratios, reproductive biology and production. Furthermore, by sampling over a 24-hr
period, diurnal movements of the shrimps will be determined.
156
Stomach samples from L. niloticus were collected from trawl catches carried out by the RV
Lake Victoria Explorer in the three zones between March and June 1999. The length of the
fish, index of fullness and volume of each food item present in these stomachs were recorded.
These data provided quantitative information on the relative importance (as compared to the
other prey species) of C. nilotica as a food source for different sizes of L. niloticus at several
localities
Results
Only one form of C. nilotica, which occurs both in the littoral waters and in deep waters at
the thermocline (inhabiting the transition zone from oxygen-rich to oxygen poor conditions
around the thermocline) was found. Offshore populations of C. nilotica were mainly
planktonic rather than benthic, and they exhibit diel vertical migrations into near surface
waters at night.
The density of C. nilotica at three stations in area A for the month of June, 1999 was 2004
md. m at Kibara (6.75 m depth), 1295 md. m at Kimbu (19.85 m depth) and 714 md. m2 in
Ukerewe (22 m depth). In terms of wet weight, it was 120 g m2, loo g m2 and 80 g m2 for
Kibara, i(imbu and Ukerewe, respectively.
The carapace length distribution indicated one mode at 5 rum CL (Fig. 1). The modal length
of C. nilotica in the stomachs of L. niloticus was also at 5 mm CL.
C'aridina nilotica was the predominant food item in the stomachs of Nile perch, being found
in approximately 50% of all fish in all sites (Table 1). The number of C. nilotica in the
stomachs of L. niloticus ranged from 4 individuals for a fish of 47,2 cm TL to 227 for a fish
of 49.8 cm TL. The importance of C. nilotica to the diet of L. niloticus declined with
increasing size of fish (Table 2). Few fish >50 cm had C. nilotica in their stomachs whereas
the stomach contents of small fish <10 cm were almost exclusively shrimps.
iscussion
Much of our current understanding of the autecology, production and ecological role of fish
population is derived from studies of the diet based on analysis of stomach contents (Windell
& Bowen, 1978). Caridina nilotica is an important component of the diet of many fish
species such as L. niloticus, O. niloticus, Schilbe intermedius Riippeli, Brycinus spp, Bagrus
docmak (Forsskäl), R. argentea and haplochromines, and thus supports fish production.
Caridina. nilotica, being a primary consumer grazing on algae and also a carnivore and
detritivore, therefore plays a vital role in the aquatic food web by transferring energy from the
lower to the higher trophic levels.
o Although basically a diatom eater, Nile tilapia can eat and digest cyanobacteria, insects
and crustaceans (Greenwood 1966; Welcomme 1968). Recently the diet has become more
diverse, including zooplankton and macrobenthos, e.g. the shrimp C. nilotica (Gophen et
a.l. 1995; Balirwa 1998).
157
Haplochromines were the main prey of L, niloticus until their demise, when C. nilotica, R.
argentea and juvenile L. néloticus became the most important species (Gee 1969; Okedi
1971; Hughes 1986, 1992; Ligtvoet & Mkurnbo 1990; Ogutu-Ohwayo 1990a; Mkumbo &
Ligtvoet 1992; C)gari & Dadzie 1988),
Rastrineobola argentea is a zooplanktivore, eating mainly planktonic crustaceans (Graham
1929; Corbet 1961; Hoogenboezem 1985). In addition to zooplankton, which was the basic
food during daytime, R. argentea take lakefly larvae (chironomids and chaoborids) and C.
nilotica whenever these are abundant in the water column. At night, adult lake flies are taken
whenever they swarm.
The percentage of L. niloticus containing C. nilotica declined from 60-85% for fish between
5 and 40 cm TL, to less than 10% for fish larger than 80 cm in length (Hughes 1986).
Caridina nilotica decreased and fish increased in importance as the predator increased in size.
The same trend was shown in the present study. Laies niloticus <10 cm TL ate exclusively
C. nilotica, but it only represented 17% of the food intake for the 71-80 cm size class.
For the period of January to August 1997, small L. niloticus less than 40 cm, 20 cm and 30
cm TL from S pche Gulf, Mwanza Gulf and Ukerewe waters respectively contained C.
nilolica in their stomachs, constituting over 90% of the diet. These findings differ from those
reported earlier (TAFIRI report 1996), where juvenile Nile perch was the major item of this
length group. They also differ from those reported by Mkumbo & Ligtvoet (1992) who found
haplochromines were the major food item in the Mwanza Gulf.
Further observations revealed that fish between 40-100 cm, 20-60 cm and 30-80 cru TL from
Speke Gulf, Mwanza Gulf and Ukerewe waters, respectively, consumed a variety of food
items including C. iilotica, juvenile L. niloticus haplochromines, R. argentea, fish remains,
Odonata, snails and Barbus profundus Greenwood.
The food web structure of Lake Victoria presently includes two major pathways:
o Trophic pathway based on new algal production: This pathway flows from primary
producers (phytoplankton) directly to fish (O. niloticus) and also to zooplankton.
Phytoplankton are also consumed by zooplankton which are preyed upon by juvenile O.
niloticus, Ghaobo rus, and R. argentea. Zooplankton, and perhaps Chaoborus, are
consumed by R. argentea.
o Trophic pathway based on detritus: Non-utilized phytoplankton sink to deeper layers
where they decompose. These degraded products are consumed by C. nilotica and other
invertebrates, which are consumed by juvenile and adult L. niloticus. Adult L. niloticus
also prey on young L. niloticus. Nile perch is the top consumer of this pathway. In the
present food web, L. niloticus is the top predator, feeding mainly on the shrimp C.
nilotica (primary consumer) and on R. argentea and juvenile L. niloticus (both secondary
consumers). The main pathways of energy are:
-via Caridina to Lates,'
-via Caridina and juvenile Lates to Lates;
158
-via insect larvae and juvenile Lates to Laies;
-via zooplankton to R. argentea and juvenile Lates to Lates;
- via Caridina to O. niloticus;
- directly to O. niloticus.
Conclusion
Recruitment is a key factor in determining the strength of cohorts. Since fish depend on C.
nilotica for their animal food component at early stages of their life, the quantity of C.
nilotica is critical to survival. Thus C. nilotica availability is an important factor determining
the relative survival of juvenile fishes.
These findings represent the preliminaiy output of a much wider study on the role of C.
nilotica in the fish production of Lake Victoria. This work will be intensified and expanded
to include information on production of C. nilotica, dici migration patterns and spatial and
temporal shifts in the diet of the major commercial fish species of the lake
Acknowledgements
The survey was funded by the European Union Lake Victoria Fisheries Research Project
(Ref: ACP-RPR 227) and the Government of Tanzania. Special thanks go to Dr Ian G. Cowx
for his supervision of the work. Also I would like to thank Mr D. Tweddle for his assistance
in the field. The skipper, crew of the RV Victoria Explorer and my colleague researchers are
also thanked for their co-operation in the field. I would like to thank my employer, TAFIRI,
for providing the working space and other logistics.
References
Balirwa J.S. (1998) Lake Victoria wetlands and the ecology of the Nile Tilapia, Oreochromis
niloticus Linne. PhD Dissertation, Wageningen Agricultural University, Netherlands.
A.A Balkema, Rotterdam.
Corbet P.S. (1961) The food of non cichild fishes in the Lake Victoria basin, with remarks on
their evolution and adaptation to lacustrine conditions. Proceedings of the Zoological
Society, London 136, 1-101.
Fiyer G. (1960) The feeding mechanism of sorne Atyid prawns of the genus Caridina.
Transactions of the Royal Society, Edinburgh 64, 21-244.
Gee J.M. (1969) A comparison of certain aspects of the biology of Lates niloticus (L.) in
some East African lakes. Revue du Zoologique et Botanique Afrique 80, 244-262.
Goldschmidt T., Witte F. & Wanink J. (1993) Cascading effects of the introduced Nile perch
on the detritivorous /phytoplanktivorous species in the sublittoral areas of Lake
Victoria. Conservation Biology 7, 686-700.
159
Graham M. (1929) The Victoria Nyanza and its fisheries. A report on the fishing surveys of
Lake Victoria (1927-1928). Crown Agents Colonies, London.
Greenwood P.H. (1966) The Fishes of Uganda. The Ugandan Society, Kampala (2nd edition).
Hoogenboezem W. (1985) The zooplankton in the Mwanza Gulf (Lake Victoria) and the food
of a zooplanktivorous cyprinid (Rastrineobola argentea). HEST report (unpubi.)
Leiden, The Netherlands.
Hughes N.F. (1986) Changes in the feeding biology of the Nile perch, Lates niloticus (L.)
(Pisces: Centropomidae), in Lake Victoria since its introduction in 1960, and its
impact on the native fish community of the Nyanza Gulf. Journal of Fish Biology 29,
54 1-548.
Hughes N.F. (1992) Nile perch, Lates niloticus, predation on the freshwater prawn, C'aridina
nilotica, in the Nyanza Gulf, Lake Victoria, East Africa. Environmental Biology of
Fishes 33, 307-309.
Ligtvoet W. & Mkurnbo O.C. (1990) Stock assessment of the Nile perch in Lake Victoria. in
CIFA, report of the fifth session of the sub-committee for the development of the
fisheries in Lake Victoria, Mwanza, Tanzania, September, 12-14, 1989. FAO Fish
Rep. 430, pp. 3 5-74.
Mkurnbo OC. & Ligtvoet W. (1992) Changes in the diet of Nile perch, Lates niloticus (L.) in
the Mwanza Gulf, Lake Victoria. H)'drobiologia 232, 79-83.
Ogari J & Dadzie S. (1988) The food of the Nile perch, Lates niloticus (L.) after the
disappearance of the haplochromine cichlids in the Nynnza Gulf of Lake Victoria.
Journal of Fish Biology 32, 571-577.
Ogutu-Ohwayo R. (1990) The decline of the native fishes of Lake Victoria and Kyoga (East
Africa) and the impact of introduced species, especially the Nile perch, Lates
niloticus, and the Nile tilapia, Oreochiromis niloticus. Envirno,nental Biology of
Fishes 27, 8 1-96.
Okedi J. (1971) Further observations on the ecology of the Nile perch (Lates niloticus) (L.) in
Lake Victoria and Lake Kyoga. EAFFRO Ann. Rep. (1970), pp. 42-55.
TAFIRI (1996) Surveys to determine the biornass and diversity of the demersal fish stocks in
Mwanza and Speke Gulfs following the ban of trawlers, beach seine and under sized
gilinets (Mimneo).
Tweddle D. & Bassa S. (1999) Preliminary observations on the use of a frame trawl in
hydroacoustic surveys. In: Report on third FIDAWOG workshop held at the Triangle
Hotel, Jinja, 29 March to 1 April 1999.
Welcomme RL. (1968) Observations on the biology of the introduced species of Tilapia in
Lake Victoria. Revue du Zoologique et Botanique Afrique 76, 249-279.
Windell I. & Bowen T. (1978) Gut content analysis In: T.B. Bagenal (ed.) Methods for
Assessment of Fish Production in Fresh Waters. IBP Handbook No.3, Oxford:
Blackwell Scientific Publications.
Witte F., Goldschmidt T., Goudswaard P.C., Ligtvoet W., van Oijen M.J.O. & Wanink J.H.
(1992a) Species extinction and concomitant ecological changes in Lake Victoria.
Netherlands Journal of Zoology 42, 214-232.
Witte F, Goldschmidt T., Wanink J.H., van Oijen M.J.P., Goudswaard P.C., Witte E., Maas
L.M. &. Bouton N. (1992b) The destruction of an endemic species flock: quantitative
data on the decline of the haplochromine cichlids of Lake Victoria. Environmental
Biology of Fishes 34, 1-28.
160
60.0
50.0
o
40.0
30.0
20.0
o
G)
a. 10
0.0
161
OKimbu (Ukerewe)
Kl barau
2 3 4 5 6 7 8 9 10
Length class (mm)
Fig. 1. Size distribution of (aridina inlolicci from two ZOflCS of Lake
Victoria in Tanzania
Table 1. Occurrence of C. nilotica as a food item in the stomachs of L. niloticus between
March and June 1999.
Date No of fish No with No with C No with No with
examined food nilotica in
the stomach
extruded
stomachs
empty
stomachs
March 1999 244 176 34 34
Apri! 1999 476 313 181 142 21
May 1999 293 92 38 163 21
June 1999 354 138 68 170 48
Table 2. Percentage occurrence of C. nilotica in stomachs of L. niloticus in 10-cm size
groups from areas A, B and C of the Tanzania sector of Lake Victoria.
162
Length group (cm)
Zone B
April
Zone C Zone A
May June March
1-lo 100 100 100 20
11-20 96 74 74 30
21-30 83 67 68 14
31-40 68 0 32 0
41-50 48 ii 26 19
51-60 42 0 25 11
61-70 20 0 14 0
71-80 17 0 0 0
81-90 0 0 0 0
91-100 0 0 0 0
>101 0 0 0 0


The role of Caridina nilotica (Roux) in the Lake Victoria fisheries with reference to Lates niloticus (L.)

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The role of Caridina nilotica (Roux) in the Lake Victoria fisheries with reference to Lates niloticus (L.)

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