The parasite fauna of characids’ (Osteichthyes: Characidae) Anambra River, Nigeria

The parasite fauna of characids’ (Osteichthyes: Characidae) Anambra River, Nigeria P. C. Echi1* and H. M. G. Ezenwaji2 1

Parasitological research unit, Department of Zoology, University of Nigeria, Nsukka, Enugu, Nigeria and 2Fisheries research unit, Department of Zoology, University of Nigeria, Nsukka, Enugu, Nigeria

Abstract Baseline information on the parasites of frequently caught species of the characids namely Hydrocynus vittatus, Alestes baremoze, Brycinus macrolepidotus and Brycinus leuciscus was investigated in Anambra River from August 2004 to July 2005. The parasites recovered were the Myxosporid, Myxobolus sp (Protozoa), Polyopistocotylids, Diplozoon ghanense and Neodipolzoon polycotyleus (Monogeneans), the Caryophyllid Caryophylleus sp (Cestoda) and Rhabdochona sp (Nematoda). The prevalence of Caryophylleus sp in B. macrolepidotus (14.2%) and A. baremoze (8.1%) as well as Rhabdochon sp and Myxobolus sp in H. vittatus (9.6% and 7.8% respectively) was relatively high (>7.0%); while the other parasite species Myxobolus sp in B. leuciscus (2%), D. ghanense in B. macrolepidotus (1.9%) and N. polycotyleus in A. baremoze (1.9%) had a much lower prevalence (2.7%). Distribution of parasites was clearly seasonal. Dissolved oxygen (8.0–14.0) mg l)1 and pH (5.5–7.0) influenced the occurrence of the parasites whereas temperature (20.1–27.5 DC) showed no much effect. Key words: abiotic factors, characids, parasites, seasonal changes

Re´sume´ Les informations de re´fe´rence sur les parasites des espe`ces fre´quemment capture´es de Characide´s Hydrocynus vittatus, Alestes baremoze, Brycinus macrolepidotus et Brycinus leuciscus ont e´te´ e´tudie´es dans la rivie`re Anambra entre aouˆt 2004 et juillet 2005. Les parasites retrouve´s sont le Myxosporide´, Myxobolus sp. (Protozoaire), les Polyopistocotylide´s, Diplozoon ghanense et Neodipolzoon polycotyleus (Monoge`nes), les Caryophyllide´s Caryophylleus sp. (Cestodes) et Rhabdochona sp. (Ne´matodes). La pre´valence de Caryophylleus sp. chez *Correspondence: E-mail: [email protected]

B. macrolepidotus (14,2%) et A. baremoze (8,1%) ainsi que de Rhabdochon sp. et Myxobolus sp. chez H. vittatus (9,6% et 7,8% respectivement) e´tait relativement forte (>7,0%), alors que les autres espe`ces de parasites, Myxobolus sp. chez B. leuciscus (2%), Dipolzoon ghanense chez B. macrolepidotus (1,9%) et Neodiplozoon polycotyleus chez A. baremoze (1,9%) avaient une pre´valence beaucoup plus faible (2,7%). La distribution des parasites e´tait nettement saisonnie`re. L’oxyge`ne dissous (8,0–14,0 mg ⁄ l) et le pH (5,5–7,0) influenc¸aient l’occurrence des parasites alors que la tempe´rature (20,1–27,5C) n’avait pas beaucoup d’effets.

Introduction Knowledge of the parasites that associate with characids in some African river basin ecosystems is scanty (Khalil and Thurston, 1973; Azugo, 1978; Smit et al., 2004). Expectedly, characids in these habitats would be exposed to over exploitation, predation, environmental contamination but parasitism. The aim of this study was to revisit the study at Anambra river as a reference point, especially as the previous attempt by Azugo (1978) in the same river basin, reported no parasite. In addition, characids have been shown to harbour parasites in other African river basin ecosystems (Abdel-Baki et al., 1998; Reed et al., 2002). Many parasites have free living stages (cysts, eggs or larvae) which have complimentary behavioural reactions to the external environment with the free living communities such as variation in temperature, DO and pH. Thus, their distribution and abundance can be modified by these conditions. Thomas (1964) stated that in spawning of Salmo trutta, levels of parasitism were directly related to the flood period (increased rains) and the hormonal levels of the fish. As an adequate supply of oxygen is necessary to support life in a body of water, a determination of the amount of oxygen provides a means of assessing the

 2009 The Authors. Journal compilation  2009 Blackwell Publishing Ltd, Afr. J. Ecol.

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P. C. Echi and H. M. G. Ezenwaji

Infection statistics of Bush et al. (1997)was used for the determination of prevalence, abundance and mean intensity.

quality of the water with respect to sustaining life. Cone et al. (1993) examined the parasites of American eels Anguilla rostrata in a region of Nova Scotia influenced by acid precipitation and tested the hypothesis that metazoan parasite communities in aquatic vertebrate hosts respond to acid stress in a manner similar to that of free-living invertebrate communities. Within the confines of an experimental watershed, species richness of eel parasite assemblages was the lowest in a stressed river of low pH and the highest in buffered waters. The results paralled those reported for free-living communities (Townsend et al., 1983; Muniz, 1991), indicating that the parasitic and free-living communities respond to stress similarly (Marcogliese and Cone, 1996).

Results All the host species except B. leuciscus harboured two parasite species, although these were different parasites. For instance, Myxobolus sp (7.8%) and Rhabdochona sp (9.6%) were recovered from H. vittatus, Diplozoon ghanense (1.9%) and Caryophylleus sp (14.2%) in B. macrolepidotus. Neodiplozoon polycotyleus (1.9) and Caryophylleus sp (8.1%) from A. baremoze while only Myxobolus sp (2.7%) was found in B. leuciscus. In addition, while protozoa, Monogenea and Cestode species infected two host specimens, the only Nematode species encountered was recovered from H. vittatus. The highest prevalence of 14.2% was recorded from Caryophylleus sp in B. macrolepidotus while the lowest (1.9%) was found in the same species with D. ghanense. The ectoparasites (Myxobolus sp, D. ghanense and N. polycotyleus) and endoparasites (Caryophyllleus sp and Rhabdochona sp) showed an interesting dichotomy in their peak period. Myxobolus sp in A. baremoze peaked in January, D. ghanense in B. macrolepidotus peaked in December; N. polycotyleus peaked in January – all in dry season. On the other hand, Caryophylleus sp and Rhabdochona sp. Peaked in June and September respectively, during the rainy season when the floodplains were full (Fig. 1). Apart from the effect of the hydrological regime on the prevalence of the parasites, other abiotic factors appeared

Materials and methods Samples of the four frequently fished species of characids – Hydrocynus vittatus, Alestes baremoze, Brycinus macrolepidotus and Brycinus leuciscus were randomly collected monthly for 12 months (August 2004 to July 2005) from caught stocks by fishers at Otuocha sampling location, Anambra river GPS (N06 21 29.211 and E06 51 21.911). Surface temperature, pH and dissolved oxygen of the river were determined in situ using mercury-in-glass thermometer, pH meter and Winkler’s method respectively (American Public Health Association (APHA), 1978). Examination of fish for parasites followed details in Arthur and Albert (1994). Procedures for treatment, fixation and preservation of parasites followed those of Ash and Orihel (1987).

Percentage prevalence

60

Nediplozoon polycotyleus in Alestes baremoze Caryophylleus sp in Alestes baremoze Myxobolus sp in Brycinus leuciscus Myxobolus sp in H.vittatus Rhabdochona sp in H. vittatus Caryophylleus sp in Brycinus macrolepidotus Diplozoon ghanense in Brycinus macrolepidotus pH DO

16 14

50

12 40

10 8

30

6

20

pH and DO

2

4 10

2 0

0 Septmber October November December January February

March

April

may

June

July

August

Fig 1 Prevalence of parasites of the characids during wet and dry seasons

 2009 The Authors. Journal compilation  2009 Blackwell Publishing Ltd, Afr. J. Ecol.

The parasite fauna of characids’ Anambra River

to influence parasite occurrence and abundance. The ectoparasites peaked in December ⁄ January when the water was slightly acidic pH = 6.6 ⁄ 6.7 and Dissolved oxygen approximately equal to 10.0 mg 1)1, whereas the endoparasites peaked in June ⁄ July when the water was definitely neutral pH = 7.4 ⁄ 7.0 and the Dissolved oxygen was approximately greater than 12 mg 1)1. Temperature appeared not to exert much effect on the parasite species recovered.

Discussion In seasonally flooding waters, dry season conditions lead to habitat contraction, lower oxygen availability and higher fish densities, and some cases lower fish condition and higher mortality (Chapman and Chapman, 1993a,b). The lower distribution of oxygen during the dry period may have arisen from waste inputs by the local population, its attendant biological activities and other characteristics of the water body. Consequently, these factors may have influenced the scanty occurrence of the ectoparasites (Myxobolus sp, D. ghanense and N. polycotyleus). Relative low pH, perhaps, affected direct life cycle of these ectoparasites. For instance, the monogenean Pseudodactylogyrus anguillae may have been sensitive to low pH, as it was found in rivers with pH greater than 5.4. The exposed state of the soft-bodied adult and the delicate, short-lived, free swimming oncomiracidium may render this parasite and others like it susceptible to harsh environmental conditions (Mackenzie et al., 1995). It can be inferred that why endoparasites (Caryophyllleus sp and Rhabdochona sp) occurred more in the wet period, during fullness of the river floodplains is because the frequency of occurrence of intermediate hosts increased during this period. Williams and Jones (1994) and Ezenwaji (2002) have reported interplay of abiotic forces (such as temperature, pH and dissolved oxygen.) as possibly being responsible for this phenomenon. Aquatic insects, which serve as intermediate hosts of the parasites, may play a vital role in this regard (Scholtz, 1991; Woo, 1995). Nevertheless, under natural conditions, parasitism may vary seasonally. According to Ezenwaji and Ilozumba (1992) Clarias sp harboured more Euchinostonum clarias and the larval spiruroid in the peak dry season months and early rainy season months than in other months. This is the period when various intermediate hosts increased in number to facilitate parasitism. During the increased rains, mollusks rapidly increased in abundance

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(Okafor, 1990) and they are readily consumed by Clarias ebriensis Ezenwaji and Ilozumba (1992)

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