Biological studies of freshwater fishes, Cyprinion acinaces and Carasobarbus apoensis, from Wadi Khadrah, Saudi Arabia

2.1 Collection of fish

Cyprinion acinaces and Carasobarbus apoensis fish samples were collected from Wadi Khadra, Medina in each month. A total of 103 samples of C. acinaces were collected, with a length ranging between 6.5 and 13.0 cm and the weight ranged between 2.62 and 24.54 g. Specimens of Carasobarbus apoensis collected were 53 and their length ranges between 10.5 and 24.5 cm and weight were from 14.05 to 167.4 g. In the laboratory, length measurements were taken. Weights were recorded in gram using the RADWAG balance.

2.2 Condition factor (K)

The Fulton coefficient (K1) and Clark coefficient (K2) were calculated from the equation used by Aday et al. (2002): $$K=\left(W/L^3\right)\times 100.$$ where: -

• K: Condition factor (K1 = with total weight) and (K2 = weight without viscera).

• W: The weight of the fish, with or without viscera, in grams.

• L: The total length of the fish in centimeters.

2.3 Hepatosomatic index (HSI)

Hepatosomatic index was calculated from the equation given by Lagler (1978): $$\mathit{HSI}=\left(\mathit{LW}/BW\right)\times 100$$ whereas: -

• HSI: Hepato-Somatic index.

• LW: Weigh the liver in grams.

• BW: Fish weight in grams.

2.4 Mathematical description of growth (Van Bertalanffy)

To calculate the growth in length the Von Bertalanffy's equation as used by Sapounidis et al. (2015) was followed: $$\mathit{TLt}=TL\infty \ast (1-ek̂\ast (t-to).$$ where:

• TLt: Fish length at time t (centimeters).

• K: Growth factor.

• to: Theoretical age when length equals zero.

• TL∞: Asymptotic or theoretical maximum length (in centimeters).

2.5 The relationship between weight and length

The relationship between weight and length was calculated by using the following formula: $$W=a{L}^b$$

W (weight) in grams, L (length) in centimeters, and a, b are constants. This relationship can be expressed logarithmically as follows (Lagler (1978)): $$\mathit{Log}W=\log a+b\log L.$$ where:

• L: Total length of fish (cm).

• W: Total weight of fish (grams).

• a, b: Two linear regression constants.

2.6 Determination of the length of fish at previous ages:

To estimate the age of the fish, the scales are cleaned and dyed with alizarin red dye, placed between two glass slides, and images are taken with a digital camera fitted to an optical microscope (Olympus Db72) and connected to a computer. The following equation presented by Sapounidis et al, 2015 was used to calculate the length of fish at previous year (back calculated lengths): $$\mathit{TLi}/TL={\left(\mathit{Ri}/Rtot\right)}^b.$$ where:

• TLi: Total length at age i.

• TL: The total length of the fish at time of catch.

• Ri: Length of the scale radius of the first year.

• Rtot: The total radius of the scale.

• b: The straight line constant.

3.1 Different indices

The seasonal variations in the values of condition coefficient of C. acinaces and C. apoensis are presented in Tables 1 and 2, respectively. The condition coefficient (K1) and the condition factor (K2) for combined sexes of C. apoensis reached the highest values (1.35 and 1.18, respectively) ​​in the winter season and the lowest values were recorded in the fall season (0.74 and 0.67). Lower values of these factors (K1 and K2) were registered in winter season (1.02 and 0.83) and maximum was reported in spring (1.22 and 0.99) for C. acinaces. The high values of the condition factor in certain period of the year are attributed to the sufficient abundance of food in the environment and high assimilation of food in the bodies of the fish. Where the high concentration of nutrients in the warm months increases the production of food items for the fish (Al-Kahem et al., 1997). The low values of the condition factor obtained in the winter season indicated the effect of the fish spawning cycle, the lower abundance of food in the environment, and the frequency rate of immature individuals in the samples (Al-Ghanim, 2005). In general, the seasonal changes in condition coefficient is affected by feeding activity; size of the fish; development of gonads, reproduction periods; parasitic loads and diseases (Welcome, 2001; Sapounidis et al., 2015; Uckun and Gokce, 2015).

The averages of the hepatosomatic index were monitored monthly and seasonally, and in the summer season the highest value was 2.53 and the lowest value was in the winter season 1.46 for C. apoensis whereas the values were maximum (3.06) and minimum (1.36) in summer and winter, respectively for C. acinaces. Inactivation of the gonads leads to an increase in the liver index values. The value of the liver index decreases during the maturation of the gonads and prevailing unfavourable physical and biological condition of the environment specially food abundance and temperature (Al-Ghanim, 2005; Ahmad, et al., 2013, Hakami et al., 2013) (see Table 3).

3.2 Length weight relationship

The relationship between weight and length is from biological studies that indicate the health status of fish and their ability to benefit from their food and other conditions in their natural environment (da Costa and Araojo, 2003). This relationship is presented in Fig. 1 for Carasobarbus apoensis and Fig. 2 for Cyprinion acinaces. The importance of these factors lies in providing information about the time of maturation of the ovaries, the extent to which the fish benefit from their food and thus the stages of their growth, which information is necessary to lay the general foundations for the use of these fish and to develop a general concept for their management on sound scientific foundations, especially when growth is homogeneous (Hakami et al., 2018). Among the factors affecting the value of the regression coefficient of fish are embryonic changes, fish nutrition, sexual maturity, age difference, diseases and parasite infection (Yildirim et al., 2001). When looking at the length and weight data for this study it was found that the value of “b” recorded in C. acinaces was 2.58 and for C. apoensis it was 2.30 which are less than the isometric value “3”. Values below the ideal value indicate various obstacles that affect fish growth, including lack of food and fluctuations in temperature, which negatively affects the growth of Fish (Uckun and Gokce, 2015; Abu El-Nasr, 2017). The b values ranges from 2.173 to 3.472 for the freshwater fishes reported by Tah et al. (2012). Zhu et al. (2021) have reported b value as 3.015 for freshwater fish. There are certain factors which affect the fish growth, such as fish size and quantity and quality of food (Handeland et al., 2008). When considering the length and weight data for this study, it was found that the value of “b” is 2.30 which is less than the hypothetical value 3, indicates that the growth was heterogeneous or negatively allometric. The results of this study are in agreement with the results of many studies that have shown that the law of cube did not fully apply to the fish that they studied as the regression coefficient was clearly less than the value of 3, and that these low values for parameter (b) may be attributed to the influence of various environmental factors that affected the growth of fish as previously mentioned (Sivakami, 1987) (see Table 4).

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Fig. 1

Length to weight relationship of Carasobarbus apoensis.

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Fig. 2

Length to weight relationship of Cyprinion acinaces.

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3.3 Age and growth

The age and growth parameters of fish have been most commonly estimated from the annual growth mark on the scale or otolith (Sapounidis et al., 2015; Abu El-Nasr, 2017; Ortego-Garcia et al., 2017; Hakami et al., 2018). The scale examination of Cyprinion acinaces and Carasobarbus apoensis have revealed that both species have a clear annuli on them. “Numerous studies on the scale structure of fishes have been undertaken in the world, and the results have been successfully used for growth studies, calculation of minimum harvestable size, and determination of age in fishes” (Rifflart et al., 2006; Abedi et al. 2011).

The formation of year-marks on the scale or other hard organs occurs mainly during the period of low feeding and may happen at different times in different fishes. The growth of fish may be affected by a number of factors prevailing in the environment such as temperature, availability of food and spawning cycle. These factors are supposed to affect the formation of year-mark specially feeding regime. Formation of annulus in rock hinder and red hinder occurred from March to May (Potts and Manooch, 1995) and in December in Barbus sharpyi (Mohamed et al., 2012).

The assessment of growth rates showed that the growth in length was higher during the first year of life. The data embodied in Table 5 for Cyprinion acinaces and Table 6 for Carasobarbus apoensis indicate that back calculated length gradually decrease in subsequent years in both the species. Same pattern of growth in length of Siganus rivulatus was reported by El-Gammal (1988). The growth pattern in the length registered in the present study for Cyprinion acinaces and Carasobarbus apoensis is similar to the previously published results.

3.4 Van-Bertalanfy growth function

The current study indicated a hypothetical mathematical description of growth in C. acinaces and C. apoensis, as their ages ranged between (1–4) and (1–7) years, respectively (Tables 6 and 7). The growth rate during the first year was the largest and with age, a decrease in the growth rate was observed, which is consistent with the study of Mohamed et al. (2012) performed on Barbus sharpyi fish. Since the value of asymptotic (L∞) length is inversely related to the growth factor K, so fish that take a long life to reach the value of L∞ have a lower value of growth constant (K) in them compared to fish of short life that often reach the value of L∞ in one or two years. This relationship was clearly observed when comparing the values of L∞ and K in the current study. The value of the final length L of fish is also affected by changes in the amount of available food and fish population density, while the K value is affected by genetic and physiological factors (Beverton and Holt, 1957). The value of asymptotic length (L∞) or weight (W∞) may be more or less than the observed length and weight values of fish. In present study the observed length values in both the species are more than the asymptotic values. Similar to present study Gonçalves et al. (2003) registered asymptotic (L∞) value smaller than the maximum length of fish and stated that this may be because of the faster growth in the first two years which is slows down afterwards. They also mentioned that slow attainable of largest size, being a characteristic of longevity. Mouine et al. (2010) and Gómez-Márquez et al. (2008) reported asymptotic values of fish more than the observed values and mentioned that mainly young individuals were the main part of the catch. Ogle and Isermann (2017) found that the asymptotic length was more in females than males, hence, the males take more time to attain maximum length than female. In present study it is clear that the C. apoensis taking more time than C. acinaces to attain asymptotic length as the growth constant (K) values are higher in acinaces than apoensis (Table 7).