Journal of Applied Sciences & Environmental Management, Vol. 8, No. 2, Dec, 2004, pp. 39-44
Determination of the infection densities of mudfish Eustrongylides in Clarias gariepinus and C. anguillaris from Bida floodplain of Nigeria
1* IBIWOYE, T I
1Pathobiology Programme, Artisanal Fisheries Division,National
Institute for Freshwater Fisheries Research (NIFFR),P. M. B. 6006, New Bussa,
Niger State, Nigeria.
Code Number: ja04022
infection densities of Eustrongylides africanus larvae were analysed
according to the season, sex and distribution. Its prevalence, intensity and
was 26.5 ± 15.4%, 2.1 ± 0.9 and 0.7 ± 0.5 worms per fish, respectively for the
wet season and the dry season had 32.9 ± 5.4%, 2.5 ± 0.4 and 0.9 ± 0.2 worms
per fish, respectively. These incidences increased greatly during the dry season,
being higher in the females than the males for both seasons of the year. Its
lifecycle is complex and indirect with fish as intermediate, reservoir (alternative)
or final (definitive) hosts. However, this is the first report and record of
the incidence and lifecycle of infections with larvae of Eustrongylides africanus in
free catches freshwater mudfish Clarias from Bida floodplain of
occurrences of helminth parasites in fishes have been extensively studied in
various water bodies in
MATERIALS AND METHODS
The study covered an area located between longitude 5o 45 to 6o 15E and latitude 8o 30 to 9o 10N within the southern Guinea Savannah zone of Nigeria (Areola et al., 1992). 2700 Clarias of different sizes, sexes, lengths and weights randomly selected were 5-10% of the catches from four sampled locations (Doko, Dokoji, Fokpo and Dutsu) in the Bida floodplain. They were handled in humane manner, thoroughly examined and dissected to recover helminth larvae, for direct numerical count using a tally counter, and the sites of infection recorded at NIFFR Fish Health Diagnostic Laboratory. Its prevalence, intensity and abundance were determined for sex and seasons of the year as described by Margolis et al. (1982).
RESULTS AND DISCUSSIONS
The prevalence of E. africanus larvae infection in Clarias from Bida floodplain is shown in Figure 1. The males prevalence of 33.7% in January decreased to 26% in June, and increased to its peak of 33% in July followed by sharp fall to lowest value of 5.4% in October with a sharp rise to 27.7% in December. The females prevalence of 42.4% in January decreased to 27.3% in April followed by a sharp rise to its peak of 50.2% in June, also with a sharp fall to its lowest value of 8.0% in October later by a sharp rise to 32.6% in December. The prevalence for the total sampled of 39.6% in January decreased to 26.7% in April followed by a sharp rise to its peak of 41.9% in June followed by a sharp fall to its lowest value of 7.1% in October later by a sharp rise to 31.1% in December. Both the females and total sampled had their peaks in June while the males had their peak in July. The trend of prevalence is about the same for the males, females and total sampled since all of them had falls in April and October. The intensity of Eustrongylides africanus larvae in Clarias of Bida floodplain is shown on Fig 2. The males intensity of 1.5 larvae per infected fish increased to 2.3 in April followed as sharp fall to 1.0 in June with characteristic rises and falls between July and to 1.3 in December.
The females intensity of 3.7 larvae per fish gradually decreased between March
and June to 2.6 followed a sharp rise to its peak of 4.1 in July also followed
by a sharp fall to 1.4 in October and later by a sharp rise to 2.5 in December.
The intensity for the total sampled of 3.0 larvae per fish in January gradually
decreased between May and April to 2.7 followed by a gradual rise to its peak
of 3.5 in July with a sharp fall to its lowest value of 1.4 in September and
followed by a rise to 2.1 in December.
It is evident that female fishes are more frequently infected with parasites than the males from the findings of this study. This observation agreed well with the findings of Mhaisen et al. (1988) that female fishes were generally more liable than males to infections with cestode, nematode, acanthocephalan, crustacean and copepod parasites. The mean prevalence, intensity and abundance of Eustrongylides africanus larvae in Clarias for the dry season is higher than the wet season of the year. Fishes are susceptible to heavy infestation with parasites mainly in the early rain when fishes are weakened by hibernation (a state of exhaustion). Larger fishes are heavily parasites than smaller ones. The intensity and prevalence of parasites infection increases with increasing length, size and age of the fish host. And that the food amount contained in the intermediate host of the parasite might cause the increase in infection level.
Eustrongylides species have complex, indirect life cycle (Yanong, 2002) with fish as intermediate, paratenic (alternative) or final (definitive) hosts. Where the fish is the intermediate host, the nematode eggs/larvae enter an invertebrate or a fish intermediate host prior to being eaten by or entering the final host. The final host (which contains the reproductive adult stage of the nematode may be a piscivorous (fish eating) fish, mammal, amphibian, reptile or bird. Where the nematode has the ability to survive in alternative organisms, known as paratenic or reservoir hosts, which are not required for completion of the life cycle, but they can contain infective nematode life stages and be a source of infection. They can be fish, worms or other aquatic organisms that can eat the nematode eggs/larvae. Where the fish is the final host, the nematode eggs/larvae enter an aquatic invertebrate intermediate host such as a copepod, annelid worm or insect larva prior to being eaten by or entering the final host fish. The eggs of all Eustrongylides species are very tough and can easily survive for some time in fishponds. At about 77°F, it can take anytime from 3 4 1/2 months from the time fish become infected. This means that, after sterilization of ponds, if fish eating birds do infect the ponds with Eustrongylides eggs, the producer may not see a problem until harvesting the fish, 3 4 months later, as this is approximately the time required for the eggs to hatch and become the L3 stage which infects the fish. After this 3 4 months period, fish raised on ponds with a population of fish eating birds have a greater chance of becoming infected as the number of nematode increase overtime. Adults are found in fish eating birds, the eggs are shed by the aquatic birds into ponds, where they develop into a life stage that is consumed by an oligochaetes or annelid worms where it develops further into a third large stage L3 which can infect fish when eaten. Once the annelid worms containing the L3 stages is eaten by a fish and digested, the nematodes migrate (within the fish) into the body cavity and, frequency, over the external surface of internal organs such as the liver. Some recent studies, however, suggest that E. ignotus, commonly found in mosquito fish, which is a close relative of Eustrongylides africanus, may be able to complete its life cycle without the need for a tubifex worm (Coyner et al., 2002). The first intermediate hosts are oligochaetes or annelid worms (Shah-Fischer and Say, 1989). Complementary (reservoir, alternate, paratenic) hosts are fish, where encysted larvae are found. The death of the host might stimulate the nematodes to emerge from their cysts, migrate through the body wall to the surface of their dead host and may survive for over 24hrs when a dampened condition exists. The specimens of fourth stage of Eustrongylides species were morphologically consistent with materials described by Lichtenfels and Pilitt (1986). Adult Eustrongylides africanus (Jaegerskiold, 1909), the only species so far reported from Africa was found and described only from the proventriculus and stomach walls of the female cormorants Phalacrocorax africanus (Gmelin) and in a wide diversity of other aquatic fish-eating birds (definite hosts). Eustrongylides are known from a diversity of fishes, mammals, amphibians, reptiles and birds (Hoffmann, 1999) and their relatively great abundance suggests they are common in the habitats where fish forage. But exceptionally rare parasites of carnivorous mammals associated with riparian or lacustrine habitats. The prevalence recorded in this study may indicate that larvae are particularly abundant in fishes and amphibians available to Rivers Kaduna and Niger and other tributaries supplying water to Bida floodplain; consistent with the potential that humans could be exposed to infection.
The authors are grateful to the Federal Government of Nigeria through the Federal Ministry of Agriculture and Rural development and National Institute for Freshwater Fisheries Research (NIFFR) New Bussa for providing the fund for this study.
Copyright 2004 - Journal of Applied Sciences & Environmental Management
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