Distribution and Associated Factors of Gyrodactylus Malalai Infestation in North African Catsh, Clarias Gariepinus in Ilorin, Nigeria

This study examined the occurrence and associated factors of Gyrodactylus malalai infestation in 30 cultured North African catsh in Ilorin, Nigeria. Four organs (gills, eyes, n and skin) were collected from each sh (resulted into 180 organs) and observed for the existence of G. malalai. Fifty percent (50%) of the sh examined were infested with G. malalai. Males (30%) sh were more affected than the females (20%). Density, intensity and index of infestation were signicantly different between males and females (p < 0.05). Fish with total length of 40.0 to 49.9 cm were signicantly infested than sh with total length of 20.0 to 29.9 cm (p < 0.05) but body weight did not signicantly affect the occurrence of G. malalai infestation (p > 0.05). Gills is most targeted organ of G. malalai infestation with higher percentage of infestation (8.33%), density of infestation (0.22), intensity of infestation (2.60), and index of infestation (3.25) than the eye with 2.22, 0.06, 1.57, and 0.43, respectively (p < 0.05). In conclusion, Gyrodactylus malalai infestations are high in North African catsh and could multiply rapidly and could lead to mortality if not properly managed. Furthermore, total length is identied as the predisposing factor for G. malalai


Introduction
Fish farming has become a robust industry in Nigeria in the last one decade, having production increased from 35,000 metric tons to 800,000 metric tons (FAO 2018). Individuals and the private sector had invested in aquaculture production involving mainly the semi-intensive and intensive systems. Also, Nigeria has a large market size for sh consumption because of her huge population (estimated at 200 million) and an inadequate sh supply had also contributed to the expansion. African cat sh, Clarias gariepinus is the most cultured sh species in Nigeria due to its growth performance and market value (Adeshina et al. 2019; Adeniyi 2020) but parasitic infections are greatly affecting its activities (Adeshina et al. 2021). Universally, parasites are enormous concern to freshwater shes in the tropical regions (Ekanem et al. 2011) and a major limiting factor to the growth of cultured sh in Nigeria (Bichi and Yelwa 2010).
Freshwater sh species are affected by many monogenetic trematodes, including Dactylogyrus species, Gyrodactylus species especially Gyrodactylus malalai. The G. malalai is a viviparous organism which releases its larvae freely into the environment and/or host, hence dominate within 24 hours. The G. malalai infection targets sh skin and gills resulting into skin de-coloration, peeling, de-scaling, dermatitis, sloughing, and high mortalities ( Collection and transportation of sh specimens A multisampling technique was adopted for this research study. The sh farms selected in Ilorin metropolis were strati ed into large, medium and small scales using strati ed methods as described by Fagbenro and Adebayo (2007). Thirty (30) African cat sh were randomly selected comprises of ten (10) sh from each strati ed group. The sh specimen collected was transported alive after purchase in their original water in a plastic container properly covered and well aerated to the laboratory at the Department of Aquaculture and Fisheries, University of Ilorin. The sex differential of African cat sh was performed using genital papillae commonly used in C. gariepinus as described by Omitoyin (2006). The sh were weighed using sensitive scale and the lengths were measured using meter board calibrated in centimeter.

Collection of sh organs
Four (4) organs (muscle, n, gill and eyes) of the sh specimen were collected for examination of G. malalai from each of the sh specimen which led to one hundred and twenty (120) samples. The ns, gills and eyes were aseptically collected while the sh muscles were trimmed carefully to expose any embedded parasite cysts. The organs were collected in triplicates. The whole gills were rinsed and examined under a compound microscope with magni cation of 10 xs, 40 xs and 100 xs. Tissue specimen from ns, eyes and gills pieces were cut, rinsed with normal saline solution and placed in 4% formalin buffer 10% for 24hrs in vials, shaken and the sediment examined under the microscope (Model: XSZ-170BN).

Parasites identi cation
All the parasites recovered from the organs of the sh specimen were manually counted and recorded.
Morphological features were used to identify the parasites as described by Ravichandran et al. (2009).

Calculation of parasitological indices
The analysis for G. malalai infestation to nd percentage, density, intensity and index of infestation were calculated by following the formula given by Adeshina et al. (2016).

Statistical analysis
Descriptive statistics were used to analyze the data, while the signi cance of parasite occurrence between males and females was analyzed using Chi-square test. Also, Mann-Whitney U test was performed for the signi cance of difference in the intensity of the infection between males and females (p > 0.05) while infestation among the organs were analyzed using one-way analysis of variance with the aid IBM SPSS, version 20. Table 1 and Figure 1 showed that 50% of the sh examined were infested with G. malalai. A total number of 82 parasites were recorded. Percentage of infestation was higher in male sh (30.0%) than the female sh (20.0%). Furthermore, density, intensity, and index of infestations were signi cantly higher in male sh when compared to the female with p-values of 0.010, 0.020, and 0.013 respectively.

Discussion
Huge sh mortality was reported in sh farms in Ilorin in the year 2020. The mortality was associated with mongenean parasites infection such as Gyrodactylus species. In this study, thirty (30) samples of Clarias gariepinus from different farms in Ilorin metropolis were observed for G. malalai infection from which 50% were infected. These parasites have been observed in Kenya from both farmed and capture sh (Otachi 2009). In the present study, male sh are more susceptible to G. malalai infection than the female; this observation is similar to the work of Goselle et al. (2008) who reported higher intensity of helminthes parasites in male sh than female sh. This may be because male sh are more active than females during the breeding period, and so are more prone to infestation by higher number of parasites infection. Physiology is the core reason for the dissimilarities in the parasitic load in sh (Aloo et al. 2004). Also, signi cantly higher intensity, density and index of parasitic infection in the male than female in this study are highly related to physiology and physiology functions of sex of the sh.
The ndings from this study indicated that the percentage, density, and index of infection were signi cantly related to the total length of sh. The percentage, density, and index of infection were observed in sh with total length ranged from 40.0 to 49.9 cm while the no infection was noticed in sh with 20.0 -29.9 cm total length. The percentage of infection in relation to length of host agrees to Chandra (1985) who reported higher abundance of Pallisentis sp in the intermediate length sh. Goselle et al. (2008) also observed higher infestation of helminthes in C. gariepinus with higher total length than shorter-sized sh, which were associated to the fact that as the sh increases in length, there is possibility of re-infestation by parasites. Similarly, Madanire-Moyo and Avenant-Oldewage (2012) reported higher parasites infestation in longer C. gariepinus. This observation may not be unconnected to the fact that sh with high total length occupies and covers wider areas of water and thus exposed it to parasites in the water column. However, sh body weight did not affect G. malalai infestation signi cantly in C. gariapinus in the present study. The nding on the insigni cant effect of body weight in this study is in contrast to the observation of Allumma and Idowu (2011) who reported higher parasites infestation in sh of higher body weight. This difference might be due to different ages of sh used in work of Allumma and Idowu (2011). The older the sh, the higher it exposed to parasites infestation due to longer period of time spent in the water column and agents in the environment; but in the case of the present study, the sh were of same age.
In addition, the distribution of G. malalai in the organs was found to be signi cantly different. Gills are most targeted organ of G. malalai infestation in the African cat sh, followed by the skin, while eye had the least occurrence. Signi cantly higher percentage, density, intensity and index of infestation observed in gills and skin in could be attributed to their exposure to the water and environment. Gill is the respiratory organs of sh, and thus its contact with water is constant, hence becomes easier to attack by parasites. The observation on higher parasite infestation in the gills and skin in the present study is in

Conclusion
This study concluded that Gyrodactylus malalai infestations are high in African cat sh, Clarias gariepinus. Furthermore, total length was identi ed as the predisposing factor for G. malalai infestation in the C. gariepinus. Due to its viviparous nature and proliferation of G. malalai, it could multiply rapidly and could lead to huge biological and economical losses if not properly managed.

Declarations
Funding: The research leading to these results received funding from Alhaji Abdulwaheed.
Con ict of interest/competing interests: The authors declare that they have no con ict of interest.
Availability of data and material: The data sets generated during and or analysed during the current study are available from the corresponding author on reasonable request.  Figure 1 Gyrodactylus malalai recovered from the gill of an infected sh (Mag. 40x)