Introduction

Fish parasitic diseases impose a major economic concern on aquaculture. In addition, 73% of the freshwater cultured species have diseases that are mainly associated with parasites (Lakra et al. 2006). Warm weather in Egypt is considered a great reason for the spread of parasites which led to many worse effects on fish (Eissa et al. 2013). In general, parasites of fishes cause serious economic losses due to high mortalities, tissue damage and retardation of fish growth (El-Asely et al. 2015). In Oba reservoir, Nigeria, infection of Clarias gariepinus Burchell, 1822 (Clariidae) by Monobothrium sp. Diesing, 1863, Tetracampose ciliotheca Wedl, 1861 (Syn: Polyonchobothrium clarias Woodland, 1925), Neoechinorhynchus rutile Müller, 1780, Anomotaenia sp. Cohn, 1900, Procamallanus pseudolaeviconchus Moravec & Van As, 2015 (Syn: P. laevionchus) and Paracamallanus cyathopharynx Baylis, 1923 Yorke et Maplestone, 1926, causes a reduction in the growth rate of the fish (Ajala and Fawole 2014).

The African catfish, C. gariepinus is parasitized by many external and internal helminth parasites including monogeneans, digeneans, cestodes and nematodes (El-Naggar and Serag 1987; El-Naggar et al. 1992, 1993; Hamada and El-Naggar 2003; Abdel-Gaber et al. 2015). The monogenean parasites of this host fish received a great deal of attention at morphological, ecological, and ultrastructural levels (El-Naggar et al. 2007, 2017, 2019; Mashaly et al. 2019). The study of host-parasite community structure all year round is important for providing data on their seasonal dynamics and subsequently the effect of environmental factors on their infection levels (Khan and Thulin 1991). Great attention has been paid to the parasite community structures of different fish hosts since the change in diversity and structure can be used as indicators of ecosystem health and integrity (Duesk et al. 1998). Mashaly et al. (2020) found that most monogeneans of the genus of Quadriacanthus Paperna, 1961 (Dactylogyridae) infesting the gills of C. gariepinus have their maximum infestation levels during spring and/or summer and their lowest levels were recorded during autumn and/or winter. Except for a few ecological studies (see Abdel-Gaber et al. 2015; Ali et al. 2020), most studies done on endoparasites of C. gariepinus were concentrated on morphological characters (El-Naggar et al. 1992; Ibrahim et al. 2008; Abdel-Gaber et al. 2016; Hussein et al. 2020).

The aim of the current work is to illustrate the community structure, monthly occurrence, and ecological parameters (prevalence, mean intensity and abundance) of parasitic helminths of C. gariepinus living in the River Nile (Damietta branch) at Mansoura City, Nile Delta. Moreover, it seems important to determine whether these parasites show monthly and seasonal changes in these parameters with the moderate change in temperature between seasons (15–31 °C) (Mashaly et al. 2020) in North Egypt. The condition factor of a fish depends mainly on the fish’s length and weight in its determination and is considered by some authors to be a good indicator of the physiological and general health conditions of the fish (Schmitt and Dethloff 2000; Lizama and Ambrosio 2002). Therefore, the present work was designed to determine this factor in addition to the host sex of C. gariepinus and investigate their possible effects on the infection levels of identified parasites.

Materials and methods

Collection of C. gariepinus

A total of 154 African catfish, C. gariepinus were caught in trammel nets monthly from March 2020 to February 2021, from the Damietta branch of the River Nile at Mansoura City (coordinates: 31°02′47.2′′ N, 31°21′12.2′′ E). The study area lies in the subcontinental climatic limit with four seasons namely, spring (March–May), summer (June–August), autumn (October—November) and winter (December—February). Living fish were delivered to the Faculty of Science aquarium, Mansoura University, in a container filled with freshwater where they were dissected and examined for helminth parasites using a stereomicroscope.

Determination of the fish’s biological parameters

The sex of each fish specimen was distinguished, by dissection of the reproductive organs and examination of external genitalia. To identify the condition factor, the fish's weight and length were measured. The fish sample condition factor (K) was calculated according to Barnham and Baxter (1998) as follows:

$$ {\text{K}} = 100{\text{W}}/{\text{L}}^{3} $$

where K = condition factor, W = weight of fish, and L = length of fish (cm).

The calculated condition factor of examined C. gariepinus was between 0.34 and 1.0. The fish samples were grouped into three classes: class I (0.34–0.56, bad condition), class II (0.57–0.79, good condition), and class III (0.80–1.0, excellent condition).

Identification of helminth parasites

Some collected helminth parasites were examined alive using a phase-contrast microscope while others were stained and prepared as whole mounts and later examined by light microscope. The monogenean parasites were identified according to Ergens (1973), the digeneans according to El-Naggar et al. (1992, 1993) and Plehn (1905), the cestodes according to Hamada and El-Naggar (2003) and Kuchta et al. (2012), and the nematodes according to Moravec (1998) and Moravec and Van As (2015).

Ecological parameters

These parameters include dominance, prevalence, mean intensity, and abundance. The dominance of intestinal parasites was determined according to Roohi et al. (2014) as follows:

$$ {\text{Dominance}} = \frac{{\text{N}}}{{{\text{N}}\;{\text{sum}}}} \times 100 $$

where N = abundance of a particular parasite species and N sum = total abundance of all identified parasite species. Niedbala and Kasprzak (1993) classified the helminth parasites into the following categories in accordance with dominance: eudominant (> 10%), dominant (5.1–10%), subdominant (2.1%-5%), recedent (1.1–2%), and subrecedent (< 1.0%) of a specific species. Individuals of each parasite species in each fish were counted. All other ecological parameters were calculated according to Margolis et al. (1982).

Statistical analysis and treatment of data

The relationship between helminth parasite infection levels in C. gariepinus and the seasons was determined using the SPSS package's One-way ANOVA (version 25 IBM). Where the significant differences are found, the Multiple Range Comparisons (Least Significant Difference) were selected from the Post Hoc tests (Tukey HSD) on the same statistical package to detect the variances between infection levels of different helminth parasites and different seasons. Additionally, the significance of differences in the helminth parasite infection levels between male and female fish was determined using the student's t-test. The selected probability levels are non-significant (p ˃ 0.05), significant (p ≤ 0.05), highly significant (p ≤ 0.01) and very highly significant (p ≤ 0.001).

Results

Community structure, monthly occurrence, dominance, and infection levels

The detected parasites are one monogenean Macrogyrodactylus clarii Gussev, 1961 from the gills, three digeneans, Orientocreadium batrachoides Tubangui, 1931, Eumasenia bangweulensis Beverley-Burton, 1962, and Sanguinicola sp. Plehn, 1905 from the intestine, two cestodes Tetracampose ciliotheca Wedl, 1861 and Monobothrioides chalmersius Woodland, 1924 from the intestine and two nematodes Procamallanus pseudolaeviconchus Moravec & Van As, 2015 and Paracamallanus cyathopharynx Baylis, 1923 Yorke et Maplestone, 1926from the stomach and the intestine.

It is obvious from Table 1 that O. batrachoides and P. cyathopharynx are present in all months of the year. However, T. ciliotheca and M. chalmersius, and P. pseudolaeviconchus are found during all months except November. M. clarii is absent during 6 months (February–June and August) while E. bangweulensis is absent throughout the year except for July, August, September, December, and February. Finally, Sanguinicola sp. occurs only during October, December, January, and February.

Table 1 Monthly occurrence of helminth parasites infecting Clarias gariepinus throughout the year
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Concerning dominance (Table 2), the digenean parasites were the most dominant species followed by cestodes and nematodes, respectively. Also, O. batrachoides, E. bangweulensis, and M. chalmersius showed a dominance value greater than 10% (eudominant species) while T. ciliotheca and P. cyathopharynx and P. pseudolaeviconchus registered a dominance value ranging between 5.1 and 10% (dominant species). However, Sanguinicola sp. recorded a dominance value of less than 1% (subrecedent species).

Table 2 Dominance (%) of the gastrointestinal parasites of Clarias gariepinus
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The overall infection rate of C. gariepinus with all detected parasites is 87.66% (Table 3). Generally, the nematode group attained the highest infection rate while the monogenean group recorded the lowest rate. The nematode P. cyathopharynx attained the highest mean prevalence while the digenean E. bangweulensis showed the lowest mean prevalence. Concerning mean intensity (Table 3) E. bangweulensis recorded the highest while Sanguinicola sp. showed the lowest. The most abundant parasite was E. bangweulensis whereas the least was Sanguinicola sp. (Table 3).

Table 3 Overall infection of C. gariepinus and overall prevalence, mean intensity and abundance of helminth parasites infecting C. gariepinus throughout the year
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Fluctuations in seasonal infection levels

Seasonal mean prevalence (Table 4)

Table 4 Seasonal fluctuations in the prevalence of helminth parasites of C. gariepinus
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T. ciliotheca, M. chalmersius, P. cyathopharynx and P. pseudolaeviconchus attained their maximum mean prevalence in winter and the minimum in summer (Table 4). In contrast, M. clarii and Sanguinicola sp. registered the maximum mean prevalence in summer and the minimum in winter. The digenean O. batrachoides attained its maximum mean prevalence in autumn and the minimum in summer while E. bangweulensis achieved its maximum mean prevalence in spring and the minimum in winter.

The digenean E. bangweulensis showed a highly significant mean prevalence between different seasons (F = 8.23, p ≤ 0.01). A significant mean prevalence was recorded for M. clarii (F = 3.88, p ≤ 0.05), and T. ciliotheca (F = 4.25, p ≤ 0.05) and non-significant mean prevalence for the other helminth species among various seasons. According to Multiple Range Comparisons, the mean prevalence of E. bangweulensis exhibited a highly significant difference between spring and summer (p ≤ 0.01) and between summer and winter (p ≤ 0.01) but was significant between summer and autumn (p ≤ 0.02). Moreover, a significant difference was documented for the mean prevalence of M. clarii and T. ciliotheca between spring and autumn (p ≤ 0.05).

Seasonal mean intensity (Table 5)

Table 5 Seasonal fluctuations in the mean intensity of helminth parasites infecting C. gariepinus
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O. batrachoides, E. bangweulensis and P. cyathopharynx attained their maximum mean intensity in spring while the minimum value for O. batrachoides and P. cyathopharynx was in summer and for E. bangweulensis in winter. In contrast, Sanguinicola sp. reached its maximum mean intensity in autumn and the minimum in spring. M. clarii recorded its maximum mean intensity during summer and the minimum in winter, while T. ciliotheca, M. chalmersius and P. psudolaeviconchus showed their maximum mean intensity in winter and the minimum in spring for cestodes and summer for P. psudolaeviconchus.

Seasonal differences in the mean intensities were very highly significant for E. bangweulensis (F = 56.203, p ≤ 0.001). According to Multiple Range Comparisons, the digenean E. bangweulensis recorded a very highly significant difference in the mean intensity between spring and summer (p ≤ 0.001), summer and autumn (p ≤ 0.001), and between summer and winter (p ≤ 0.001). Contrary, there was no significant difference between the mean intensities of the studied parasite species according to the One-way ANOVA test.

Seasonal mean abundance (Table 6)

Table 6 Seasonal fluctuations of the mean abundance of helminth parasites of C. gariepinus
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The helminth parasites E. bangweulensis, P. cyathopharynx, and P. pseudolaeviconchus recorded their maximum mean abundance during spring and the minimum during summer for P. pseudolaeviconchus and winter for both E. bangweulensis and P. cyathopharynx. T. ciliotheca, M. chalmersius and O. batrachoides showed their maximum mean abundance in winter and the minimum in spring for T. ciliotheca, M. chalmersius and summer for O. batrachoides. M. clarii reached its maximum mean abundance in summer and the minimum in winter while Sanguinicola sp. attained its maximum mean abundance in autumn and the minimum in winter.

E. bangweulensis recorded very highly significant seasonal difference in the mean abundance (F = 16.732, p ≤ 0.001) while T. ciliotheca recorded a significant seasonal difference (F = 3.940, p ≤ 0.05). According to Multiple Range Comparisons, E. bangweulensis showed a highly significant difference in the mean abundance between spring and summer (p ≤ 0.01), summer and autumn (p ≤ 0.01), and between summer and winter (p = 0.002). Additionally, a significant difference was noticed for T. ciliotheca between spring and summer (p ≤ 0.05).

Host sex and parameters of infection levels (Table 7)

Table 7 Mean prevalence (%), mean intensity and mean abundance of parasites infecting males and females of Clarias gariepinus
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M. clarii and P. cyathopharynx showed their maximum mean prevalence values in females while that of the remaining helminth parasites were in males (Table 7). The mean intensity of Sanguinicola sp., T. ciliotheca, and P. pseudolaeviconchus showed their maximum intensity in males and the remaining parasites M. clarii, O. batrachoides, E. bangweulensis, and M. chalmersius were in females. The nematode P. cyathopharynx recorded the same mean intensity in both males and females. The mean abundance of M. clarii, Sanguinicola sp., T. ciliotheca, and P. pseudolaeviconchus was higher in males while O. batrachoides, E. bangweulensis, M. chalmersius, and P. cyathopharynx showed maximum values in females.

P. pseudolaeviconchus was the only parasite to show a significant difference between males and females in the mean intensity and mean abundance (p ≤ 0.05) while all helminth parasites of C. gariepinus had no significant difference in their mean prevalence between males and females (p ˃ 0.05).

The condition factor and infection level parameters (Figs. 1, 2, 3)

Fig. 1
figure 1

Mean prevalence of helminth parasites infecting different condition factor classes of Clarias gariepinus

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Fig. 2
figure 2

Mean intensity of helminth parasites infecting different condition factor classes of Clarias gariepinus

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Fig. 3
figure 3

Mean abundance of helminth parasites infecting different condition factor classes of Clarias gariepinus

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The mean prevalence of M. clarii and M. chalmersius rises when the condition factor of the host increases. However, the highest mean prevalence was detected in class II for O. batrachoides, E. bangweulensis, and P. cyathopharynx while the lowest was recorded in class II for Sanguinicola sp., T. ciliotheca, and P. pseudolaeviconchus (Fig. 1). T. ciliotheca, M. chalmersius, and P. pseudolaeviconchus showed a highly significant difference in their mean prevalence between various classes of the host condition factor (p ≤ 0.01) while E. bangweulensis showed only a significant difference (p ≤ 0.05). However, for all other helminth parasite species, there was no significant variation in the mean prevalence between various condition factor classes (p ˃ 0.05).

For the monogenean M. clarii, the mean intensity increases with the increase of the host condition factor while the mean intensity of Sanguinicola sp. and P. pseudolaeviconchus declines as the host condition factor increases. However, the maximum mean intensity was detected in class II for O. batrachoides, E. bangweulensis, T. ciliotheca, M. chalmersius and P. cyathopharynx (Fig. 2). Statistically, M. chalmersius showed a highly significant difference (p ≤ 0.01) in its mean intensity between different classes of the host condition factor, while all other parasite species showed a non-significant variation in the mean intensity over different classes of the host condition factor (p ˃ 0.05).

Concerning the mean abundance, M. clarii showed a rise in its mean abundance as the host condition factor increased (Fig. 3). The maximum mean abundance was detected in class II for O. batrachoides, E. bangweulensis, M. chalmersius, and P. cyathopharynx, but the minimum mean abundance was recorded in class II for the other parasite species. All studied parasitic helminths recorded a non-significant variation in the mean abundance between various classes of the host condition factor (p ˃ 0.05).

Discussion

The African catfish C. gariepinus was found to harbor one monogenean M. clarii, three digeneans O. batrachoides, E. bangweulensis, and Sanguinicola sp., two cestodes T. ciliotheca and M. chalmersius, and two nematodes P. cyathopharynx and P. pseudolaeviconchus at the Damietta branch of the River Nile. Sanguinicola sp. is recorded for the first time in this locality in Egypt. However, it was previously described as Sanguinicola clarias Imam et al. 1984 from C. gariepinus captured by local fishermen in two other aquatic habitats of Egypt, Cairo Governorate (lower Egypt) by Imam et al (1984) and Beni-Suef Governorate (Upper Egypt) by Imam and El-Askalany (1990). There is a need for more morphological and molecular studies of Sanguinicola sp. to get a precise identity of this parasite using more advanced types of equipment like Scanning Electron microscopy (SEM). All other currently identified parasites were previously recorded in the same locality by many authors (see El-Naggar and Serag 1987; El-Naggar et al. 1997, 1992, 1993; Hamada and El-Naggar 2003; El-Tantawy et al 2018). Although El-Tantawy et al. (2018) have recorded Allocreadium sudanensis Saoud, Abdel-Hamid and Ibrahim, 1974 from the Damietta branch of the River Nile, no trace has been found of this parasite in the present study. It was interesting to note a complete absence of some helminth parasites from parasitic fauna of C. gariepinus from the Damietta branch of the River Nile and their occurrence on the same host in other communities along the River Nile. Abdel-Gaber et al (2016) described 2 digenean intestinal parasites Pseudoholorchis clarii Bayoumy, Abd El-Monem and Abd El-Atti 2013 and Glossidium pedatum Looss 1899 from C. gariepinus of the River Nile in Beni-Suef Governorate. None of these parasites was detected in the present study or other studies carried out in the present locality. In Manzala lake, Abdel-Gaber et al (2015) recorded only 4 helminth intestinal parasites from C. gariepinus: P. pseudolaeviconchus, Camallanus polypteri Kabre and Petter 1997 (Camallanidae), T. ciliotheca Woodland 1925 (Ptychobothriidae), and O. batrachoides. However, C. polypteri was not observed in the present study. Ali et al (2020) detected only two gastrointestinal parasites T. ciliotheca and P. pseudolaeviconchus, from C. gariepinus in Qaluobaya Governorate near Cairo. These variations in the community structure of intestinal helminth parasites infecting the same host that inhabits different localities in Egypt could be attributed to the variations in water physicochemical parameters and to the occurrence or absence of the parasite intermediate host.

Except for Sanguinicola sp. and E. bangweulensis, most digeneans, cestodes, and nematodes of C. gariepinus were recorded throughout the year, this indicates that the host fish C. gariepinus is highly susceptible to helminth parasite infection. However, the gill monogenean parasite M. clarii was missing during 6 months of the year (February to June and August) and the digenean Sanguinicola sp. was absent in all months except October, December, January, and February. A similar long absence of M. clarii was recorded by Hagras et al. (1999) in the same locality but during December, January, February, and April. The variation in the missing months for M. clarii from the same locality along different years indicates that there is no regular pattern for this behaviour which can be affected by the water environmental condition, the size (length and weight) of the collected host fish (Hagras et al. 1995) and/or to the reproductive activity of the parasite that may be affected by the temperature. The long missing of Sanguinicola sp. for 8 months of the year and its occurrence in the coldest months could be related to its life cycle, particularly the intermediate host.

Among the intestinal parasite groups of the present study, the digenean group was the most dominant followed by the cestode and nematode groups, respectively. Most gastrointestinal parasitic species were eudominant or dominant except P. pseudolaeviconchus and Sanguinicola sp. which were subdominant and subrecedent, respectively (Kasprzak and Niedbala 1993). In this respect, the present dominance pattern resembles that reported by Allam et al. (2023) where the digenean parasites of the African catfish Bagrus spp. Fabricius, 1775 (Bagridae) are more dominant than nematodes. However, Groenewold et al. (1996), noticed that the dominance of both the digenean Cryptocotyle lingua (Creplin, 1825) Fischoeder, 1903 (Herophidea) and the nematode Hysterothylacium sp. Ward and Magath, 1917 (Anisakidae) are greater than that of the other helminth parasites infecting the intestine of four fish species inhabiting the Wadden Sea. In contrast, Li et al. (2009) found that the nematode Procamallanus fulvidraconis Li, 1935 was the dominant species of the catfish Pelteobagrus fulvidraco Richardson, 1846 (Bagridae) in all lakes of the Yangtze River in China. Moreover, the nematodes were found to be the dominant gastrointestinal parasite species of the white croaker Micropogonias furnieri Desmarest, 1823 (Sciaenidae), from Rio de Janeiro, Brazil (Alves and Luque 2001).

It is noteworthy that the catfish C. gariepinus recorded a considerably high overall infection rate with parasitic helminths (87.66%). A similar high infection rate (78.82%) of helminth parasites was recorded for C. gariepinus at Abbasa fish farm in El-Sharkia Governorate Egypt by Radwan et al. (2021) who attributed this to the feeding habit of the catfish (bottom-feeding carnivores). This behaviour may aid in rising a load of gastrointestinal parasites by feeding on aquatic creatures that contain the infective stages of these parasites. The high rate of helminth parasite infection (65%) of C. gariepinus at Manzala Lake was attributed by Abdel-Gaber et al. (2015) to the high contamination level of the Lake by many pollutants that were poured into the lake from numerous drainage canals. Mgbemena et al. (2020) found that human-caused contamination of the Chanchaga River was the reason for the high overall prevalence of endoparasites for Tilapia zillii Gervais, 1848 (Cichlidae) (91.2%) and C. gariepinus (88.2%). Mashaly et al. (2020) reported that Manzala Lake has more chlorides, sulphates, total dissolved solids, lead, cadmium, and sodium than was typically permitted. However, the Damietta River Nile branch recorded a higher mean value of dissolved oxygen (DO) than that of Manzala Lake (Mashaly et al. 2020). Water-dissolved oxygen is regarded as a crucial component for aquatic fauna survival and is used as an indicator of a healthy environment. In the current work, the infection rate of C. gariepinus with helminth parasites in the Damietta River Nile branch is apparently higher than that recorded by Abdel-Gaber et al (2015) for the same host at Manzala Lake which means that factors other than pollution can cause the high infection rate.

The nematode parasites of the present study attained the highest infection rate over the digeneans and cestodes while the monogenean M. clarii recorded the lowest infection rate. These data resemble the results reported for the helminth parasites of the same host by Abdel-Gaber et al. (2015) at Manzala Lake and Kawe et al. (2016). However, in Qaluobaya Governorate, Egypt, Ali et al. (2020) found that the cestode T. ciliotheca had prevalence higher than that of P. pseudolaeviconchus. Some authors suggested that ingestion of copepods and molluscs by C. gariepinus may be the reason for the high infection rate of C. gariepinus by cestodes as they act as intermediate hosts for the larval stages of many cestodes (Paperna 1996; Eyo et al. 2013; Biu and Akorede 2013; Eyo and Iyaji 2014).

The level of parasitic infections of the examined parasitic helminths, in the current work, varied seasonally, but no overall significant pattern was noticed, and each parasite species reacted differently towards the seasonal changes over the study period. However, E. bangweulensis was the only parasite to show a highly significant difference in all ecological parameters between different seasons whereas T. ciliotheca showed a seasonal significant difference only in the mean prevalence and mean abundance. The cestodes showed their maximum mean prevalence and mean intensity in winter while the nematodes in spring and/or winter. With rare exceptions, spring and/or autumn were the seasons when digeneans attained their highest infection level. However, the monogenean M. clarii registered its highest infection levels in summer. These data resemble those obtained by El-Tantawy et al. (2018) who proved that most helminth parasites infecting C. gariepinus of the Damietta branch of the River Nile and Mansouria Canal have an increased infection level from winter to spring, However, Mashaly (2014) found that most intestinal parasites had their highest prevalence and mean intensity during spring or summer seasons. At Abbasa Fish Farm, in EL-Sharkia Governorate, Radwan et al. (2021) reported the highest parasitic infection of C. gariepinus with helminth parasites in summer. The low infestation level of M. clarii in winter months was attributed by Hagras et al. (1999) to the decline in temperature which strongly affects the reproductive activity of these viviparous parasites and to the increased immune response of the host at low temperatures.

All helminth parasites of C. gariepinus showed no significant difference in their mean prevalence between males and females while P. pseudolaeviconchus was the only parasite to show a significant difference between males and females in the mean abundance and mean intensity. Nevertheless, most parasitic helminths in the current investigation have a higher prevalence in males and a higher mean intensity in females. A similar result was recorded for parasitic helminths of C. gariepinus in Qaluobaya Governorate (Ali et al. 2020), and in the Lekki lagoon, Nigeria (Akinsanya and Otubanjo 2006). However, Abdel-Gaber et al. (2015), recorded a higher prevalence in females although there was no significant difference in the infection rate between the sexes. In North-central Nigeria, Ayanda (2009) found that both males and females of C. gariepinus had a similar prevalence of intestinal helminth infection. The present and previously recorded variations in the infection levels between males and females of C. gariepinus support the suggestion of the presence of other factors that can affect the infection level of these parasites. Allam et al. (2023) suggested the following factors: host biotic parameters (size and feeding habit) and water abiotic factors (physicochemical parameters, heavy metals concentration, pH, oxygen, and temperature).

The present investigation showed variations in the relationship between helminth parasite infection levels and proposed classes of host condition factor. No specific pattern can be seen. However, higher values for all infection parameters of O. batrachoides, E. bangweulensis and P. cyathopharynx were recorded in the class II host condition factor than in other classes. Moreover, a highly significant difference in the mean prevalence between different host classes was detected for T. ciliotheca, M. chalmersius and P. pseudolaeviconchus while a significant difference in the mean prevalence was noticed for only E. bangweulensis. This is a good indication that the host condition factor may influence the level of infection of parasitic helminths. An increase in the prevalence of parasitic helminths was reported by Mansour et al. (2003) as the host size increases. Abdel-Gaber et al. (2015) found no significant difference in the parasitic infection among the three size classes of C. gariepinus at Manzala Lake, although fish of larger sizes had more infections. Similar data were reported by Allam et al. (2023) for the parasitic helminths of Bagrus spp. in the Damietta River Nile branch. In contrast, Tasawar et al. (2007) and Kawe et al. (2016) showed that smaller fish had a greater parasite load. Mgbemena et al. (2020) attributed the higher prevalence value of helminth parasites on big-sized fish to their feeding habit.