Background

The African scarping feeder Varicorhinus beso is native to Ethiopia and widely distributed in other water bodies of Ethiopia (Getahun, 2010). It is distributed in the Abay basin, Awash River systems, Lake Tana, Blue Nile and Tekeze basin part of Ethiopia (Getahun, 2010; Vijverberg et al., 2012; Awoke, 2015). Particularly, it is widely distributed in upper head of Blue Nile, Beles, Gilgel Beles, Ardi, Beshilo, Gendwuha, Guang, Shinfa, Ayima, Angereb, Sanja Rivers and Tekeze Reservoir (Berie, 2007; Beletew, 2007; Awoke, 2015). Labeobarbus nedgia is endemic to Lake Tana and widely distributed in other water bodies of Ethiopia (Nagelkerke and Sibbing, 1997). It is distributed in the Abay basin and Tekeze basin part of Ethiopia, of which Lake Tana harbors the largest number of big barb species (Vijverberg et al., 2012; Awoke, 2015). Particularly, it is widely distributed in upper head of Blue Nile, Beles, Gilgel Beles, Ardi, Beshilo, Gendwuha, Guang, Shinfa, Ayima, Angereb, Sanja Rivers and Tekeze Reservoir (Berie, 2007; Beletew, 2007; Awoke, 2015). Labeobarbus species were commercially important by including Labeobarbus nedgia and therefore collectively they contributed 63 kg/trip in 1993, 28 kg/trip in 2001 and 6 kg/trip in 2010 in Lake Tana (Dejen et al., 2017). The African catfish Clarias gariepinus is widely distributed in African freshwater and Middle East (Clay, 1979; Viveen et al., 1986; Spataru et al., 1987). In Ethiopia, it is widely distributed almost in all water bodies such as in the rift valley, Abay, Awash, Baro-Akobo, Omo-Gibe, Tekeze and Wabishebele-Genale basins (Golubtsov and Mina, 2003; Awoke, 2015). It also contributes to the Ethiopian capture fisheries (Reyntjens and Wudneh, 1998).

Length-weight relationship (LWR) is very important for proper fish utilization and management of the fish population and it is possible to estimate the average weight of fishes at a given length (Lawson et al., 2013). Furthermore, the length-weight relationships among the fish population indicates that their wellness (Hamid et al., 2015). The difference in length-weight is obtained by the biotic and abiotic environmental factors as well as the trophic status of a given aquatic ecosystem. Condition factor is good parameter that shows the wellbeing of fishes in their natural habitat or in aquaculture and it is represented as by the coefficient of body condition. It is an indicator of different biological and ecological factors in relation to fishes feeding habits (Nehemia et al., 2012). Better body condition is correlated with high values of condition factor. Similarly, poor body condition is obtained when the values of condition factor is less (Gupta and Tripathi, 2017). Although, it is influenced by stress, sex, season, availability of food and the water quality in the environment in which they live (Ighwela et al., 2011).

Length-weight relationship and condition factor data on a given fish population are vital parameters for stock assessment, because they provide important information (Olabode et al., 2007; Shalloof et al., 2009) in both wild and controlled environments. In addition, the information is vital to enhance the knowledge of the natural history of commercially important fish species like L. nedgia, V. beso and C. gariepinus for conservation. The length-weight relationship and condition factor of L. nedgia, V. beso and C. gariepinus have been reported from several water bodies (Tesfaye, 2006; Beletew, 2007; Gebremedhin et al., 2012; Melaku et al., 2017) and (Alemayehu, 2009; Abera et al., 2014; Abera, 2016) respectively. However, there is no summarized information on the length-weight relationship and condition factor of these three species in different Ethiopian water bodies. Therefore, this review paper is aimed to evaluate the length-weight relationship and condition factor of the endemic Labeobarbus nedgia, the native varicorhinus beso and the African catfish Clarias gariepinus in Ethiopian lentic and lotic water bodies.

1 Materials and Methods

Data sources were collected from January, 2018 through February, 2018. A range of literature sources were used for this review including journal articles, books and book chapters, workshop proceedings, FAO reports, bulletins, legal documents, and unpublished reports including PhD dissertations. The documents were collected from University libraries and Ethiopian Ministry of Livestock and fishery, from individual researchers, and from the Internet data bases.

1.1 Some biological aspects of the three commercially important fishes in Ethiopian water bodies

1.1.1 Length-weight relationship

The wellbeing of fishes is determined by the length-weight structured data (Hamid et al., 2015). Because of, it can predict the average weight of the fish at a given length group by establishing a mathematical relation between length-weight (Ahmed et al., 2017). Based on this, fishes can achieve isometric, negative allometric or positive allometric growth pattern throughout its life (Nehemia et al., 2012). Isometric growth pattern (b=3) is all the body parts grow at nearly the same rate as the fish increases in size. Therefore, nearly isometric growth pattern was reported in Geba and Sor Rivers (Melaku et al., 2017), Beshilo River (Beletew, 2007), Arno-Garno River (Gebremedhin et al., 2012), Angereb and Sanja Rivers (Tesfaye, 2006) for L. nedgia fish species and in Lake Hayq (Alemayehu, 2009), Lake Ziway (Abera et al., 2014; Abera, 2016) and in Lake Babogaya (Abera et al., 2014) for C. gariepinus (Figure 1)

Positive allometric growth (b>3) in which fish become relatively deeper-bodied as it increases in length (Riedel et al., 2007) and therefore, Varicorhinus beso had positive allometric growth pattern in Dura and Ardi Rivers (Beletew, 2007) (Figure 1).

The differences in regression coefficient b (growth parameters) might be due to seasonal fluctuations in water quality parameters, food availability, feeding rate, gonad development and spawning period (Bagenal and Tesch, 1978). According to Fulton (1904) the growth performance of fish could vary in different places and at certain times of the year and this is due to variations in biological factors, such as availability of foods, quality and quantity of food, feeding rate and spawning period of fish affects the b value of fishes (Suquet et al., 2005). According to Wotton (1995), the coefficient of length weight relationship value (b) is used as an indicator of food availability and growth pattern, where the feeding availability is influenced by spatial and temporal variations of foods. In addition, to the variation between habitats, physiological and biological factors of the fish affect the fish growth (Zdanowski et al., 2001). The gonad development also affects the fish weight and b values in the length-weight relationship (Wotton, 1995; Zdanowski et al., 2001). In case of season variations Beletew (2007) stated that the weight of the fishes is higher in the wet season than the dry. Because the wet season is the time of active feeding for most riverine fish population. This is due to eutrophication that the flood brings external nutrients into water bodies which promote the growth of aquatic flora and fauna which are the source of fish food items. Indeed, gonad development, fat deposit accumulation and the fish become heavier in the wet season. Similarly, the differences of the length weight regression coefficient value b values between the species and other fish species obtained by seasonal, even daily, habitat differences, the degree of stomach fullness, maturity of the sex organs, and the condition of the fish health (Gupta and Tripathi, 2017).

1.1.2 Fulton Condition Factor (FCF)

Condition factor expresses the degree of wellbeing of fishes in their habitat. On the other hand it is a measure of various biological and ecological factors with regard to their feeding conditions (Nehemia et al., 2012). Food availability in the water bodies are influenced by the changes in the water chemistry due to variations in the atmosphere and the surrounding environments (Pothoven et al., 2001). Varicorhinus beso, L. nedgia and C. gariepinus had varied condition factors in different water bodies of Ethiopia. Based on this, L. nedgia and V. beso had good body conditions in Angereb and Sanja Rivers (1.18, 1.05) (Tesfaye, 2006), Geba and Sor Rivers (1.09, 1.03) (Melaku et al., 2017) and in Dura (1.1), Ardi (1.02) and Beshilo (1.09) Rivers respectively than C. gariepinus in Lake Hayq (0.69) (Alemayehu, 2009), Lake Babogaya (0.64) (Abera et al., 2014), Lake Ziway (0.76) (Abera, 2016) respectively (Figure 2). Ighwela et al. (2011) stated that seasonal fluctuations in food quantity and quality, water level, flow rate and temperature affect the condition factor of fishes. The measure of fish condition factor is determined by various factors. According to Otieno et al. (2014), it changes in abundance of food and water quality, and fluctuation of water level and water temperature determine the body condition of fishes. Condition factor also shows variation that happens seasonally due to sex and gonad development (Engdaw, 2014). This is because large part of energy is allocated for growth and emptying of ovaries, which results in the lower body condition of fish (Abera et al., 2014). The higher body condition indicates the higher energy content, adequate food availability, reproductive potential and favorable environmental condition (Pauker and Rogers, 2004).

Clarias gariepinus in Hayq, Babogaya and Ziway Lakes had the poor body condition as compared to the V. beso and L. nedgia fish species in some other rivers of Ethiopia. The differences in body condition obtained might be due to differences in environmental condition, quantity and quality of food, feeding rate and water level fluctuation. This is because most of the Ethiopian lakes are under high human pressure, mainly using the lake for agricultural activities (Gebretsadik and Mereke, 2017) and impact of water hyacinth (mainly observed in Lake Tana and some other Ethiopian rift valley lakes), expansion of agriculture and industrialization, climate change, using improper fishing gears and poison plants, wetland degradation and fish diseases. As a result the water is getting shallower and shallower, which is not comfortable for the bottom feeder fishes like C. gariepinus. This could result the poor body condition of fish in the water bodies. V. beso and L. nedgia had good body conditions in rivers of Ethiopia. This is most probably running waters receive significant nutrient inputs like nitrogen (N) and phosphorus (P) by eutrophication (loading of nutrients). In addition, the seasonal flooding can contribute to high zooplankton population in the water through bringing nutrients from the environment, and help in mixing autochthonous nutrients amongst the different strata of lake, which trigger the fauna and flora to increase the productivity of water bodies (Okogwu, 2010).

2 Conclusions

Based on this review the length-weight relationship and condition factor of the endemic Labeobarbus nedgia, Varicohrinus beso and the African catfish Clarias gariepinus were different in different water bodies of Ethiopia. Labeobarbus nedgia and Clarias gariepinus showed isometric growth pattern in most water bodies of Ethiopia. Whereas, V. beso had positive allometric growth pattern in Dura and Ardi Rivers. Labeobarbus nedgia and V. beso had better body condition than C. gariepinus in all water bodies. In conclusion, the biological aspects of fish (the body condition and length-weight) ultimately depend on seasons, sex, food availability, water quality parameters and gonad development in the water bodies to be considered. Therefore, proper management of aquatic ecosystems is vital for sustainable fish stock utilization in the country.

Authors’ contributions

Agumassie Tesfahun has compiled the data, prepared the manuscript, edited and finalize of the manuscript.

Acknowledgements

I acknowledged the efforts made by the earlier researchers and express my gratitude for permitting to use the required data from their publications.

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