Age and growth of oriental sole , Brachirus orientalis ( Bloch & Schneider , 1801 ) , in the Persian Gulf ( Soleidae )

Editor: Rubens M. Lopes The age and growth parameters are important biological indices in fish biology, fishery management, and aquaculture (Ghanbarzadeh et al., 2013, 2014, 2017). In practice, the age and growth parameters of fish are typically studied by examining catches at monthly intervals (Keivany et al., 2012; Keivany and Daneshvar, 2016). Soleid fish (family Soleidae from the order Pleuronectiformes) is one of the important groups in the Persian Gulf, as they are consumed by people inside Iran and are also exported to the adjacent countries. However, there is little information on their biology. Seventeen species belonging to five families have been reported for the region (Yasemi et al., 2008). Brachirus orientalis (Figure 1) is widely distributed in the Persian Gulf and Makran Sea. They mostly live at depths of 10-200 m (Randall, 1995), reaching 40 cm in length and 1 kg in weight (Carpenter et al., 1997). Since soles are usually by-catch from shrimp trawls and other fishing nets, they have been neglected in biological studies in the region. Mohammadi and Khodadadi (2008) studied the growth parameters of B. orientalis, Bagherpour et al. (2011) examined the parasitic infections, and Moghdani et al. (2014) investigated the effects of petroleum pollution on nickel concentration in sole muscle tissue. Thus, this study aimed to obtain some information on the age https://doi.org/10.1590/s2675-28242020068317

This study was performed from August 2015 to July 2016. The samples were obtained from commercial bottom trawls; 30 random samples were collected per month and transferred to the laboratory for further studies. The total (TL) and standard (SL) lengths were measured to the nearest 0.1 mm and total weight (TW) to the nearest 0.01 g. To determine the age, the fish otoliths were removed, washed in water, and dried and cut after embedding in resins (Campana and Neison, 1985).
The parameters of the length-weight relationship (LWR) were calculated for both sexes and for the whole sample by fitting the power function to the length and weight data using equation W=aL b (Pauly, 1984). The t-test was used to determine if the b value was significantly different from 3.
The growth was modeled using the von Bertalanffy (1938) growth equation for length L t = L ∞ [1-e -k(t+t 0 ) ] and weight W t = W ∞ [1-e -k(t+t 0 ) ], where L t is the total fish length at age t, L ∞ is the asymptotic total length, K is the growth coefficient, and t 0 is the hypothetical age when fish would have been at 0 cm total length, W t is the total fish weight at age t and W ∞ is the asymptotic total weight. The maximum age (t max ) that a fish would reach, was calculated using von Bertalanffy growth function as t max = t 0 +3/K (Taylor, 1958). The condition factor was measured using the equation Cf=(W/L 3 )×100, where, W = weight of fish (g), L = length of fish (cm), a = intercept, and b = slope (Bagenal and Tesch, 1978). The growth performance index was calculated as Ǿ= LnK+2LnL ∞ . The Instantaneous growth rate was calculated by G= (lnW t+1 -lnW t )/∆t in females and males. The natural mortality rate was estimated based on Pauly's (1984) empirical equation at average temperature of 22°C for length as: and for weight as The statistical differences between the means were determined by t-test for independent samples. The chi-square test was used to test for deviation of the sex ratios from the expected 1:1 ratio. The relationship between length and weight was tested with a regression analysis and the degree of association between them given by the coefficient of determination (r 2 ). All the statistical analyses were performed at the 95% confidence level using Excel 2016 and SPSS 20 computer software.
Of the 300 individuals studied, 205 were females (68%) and 95 were males (32%), indicating a sex ratio of about 1M:2.2F (= 40.33, df= 1). The total length and weight of the specimens ranged between 14.  (Figure 2). There were significant differences in female and male lengths and weights (p<0.05).
The length-at-age analysis indicated the growth parameters as L ∞ = 36. The life span or maximum age was calculated as 17.5 years in females and 20.8 years in males. The Ǿ value was calculated as 5.45 in females and 5.12 in males. The overall instantaneous growth rate was calculated as 0.04 in females and 0.06 in males. The natural mortality rate was estimated based on length as 0.49 in females and as 0.59 in males and based on weight as 0.59 in females and as 0.53 in males at the average temperature of 22°C.
The maximum total length and weight for this species were 38.5 cm and 757 g in females. Yasemi et al. (2005) reported the maximum length and weight of this species as 27.6 cm and 696 g, and Mohammadi and Khodadadi (2008) reported the maximum length as 40 cm. There was a significant difference in the total length and weight of the males and females at different ages. The maximum age in this study was 17 + years and the most frequent age classes were 6 and 7 years (Table 1). There is no other age data for this species to compare. However, the differences and discrepancies in age composition could be due to fishing gears, different age determination methods, ecological conditions, and population differences (Evans, 1998;Kiani et al., 2016;Keivany et al., 2018).
The LWR implied that the growth was negatively allometric in all the specimens of this study. The different growth strategies are of influential factors on the LWR. The LWR was originally used to provide information on fish conditions and may help determine whether the somatic growth is isometric or allometric (Ricker, 1973). In Cynoglossus arel, the LWR was estimated as W= 0.257TL 1.8 in the Persian Gulf (Nasri and Taati, 2010). In Pseutodes erumei, it was reported as W= 0.005TL 3.284 (Azh et al., 2013).
Generally, the b value lies between 2.5-3.5 and is affected by seasonal, geographical, feeding, and environmental conditions (Weatherley and Gill, 1987;Keivany et al., 2017).
In this species, as in other related species (e.g., Türkmen, 2003), the L ∞ was higher in the females. This difference can be due to older age at maturity and longer life span of females. The earlier maturity in the males leads to the slower growth of the somatic organs (Wootton, 1998;Keivany et al., 2014). However, they rarely reach the asymptotic length in the wild due to the natural causes such as predation, diseases, and fishing (Biswas, 1993).
The growth performance index was higher in females, indicating their faster growth rate. The higher growth rate means that the fish reaches the asymptotic length faster (King, 2007). These parameters are influenced by temperature, salinity, dissolved oxygen, and other environmental conditions, thus varying with these factors. Besides, as temperature increases, K increases logarithmically, and L ∞ decreases (King, 2007). Also, K was higher in females than that in the males. t 0, which depends on L ∞ and K, was lower in females, indicating a faster growth rate (Sparre et al., 1989(. The growth varies with temperature and feeding conditions, which affect the physiology of the fish (Grossman et al.,     1980; Bruton, 1990). This species reaches a larger size and older age in colder waters despite later maturity (Ross, 1988). The growth parameters are affected by biological production, genetics, and fishing gears (Pauly and Munro, 1984;Pajuelo and Lorenzo, 2003). The mean condition factor was higher in females. The condition factor is an indicator of the effect of interaction between biological and non-biological factors on fish physiology and is used to compare different populations in different conditions and life cycles (Bagenal and Tesch, 1978;Asadollah et al., 2017). In general, B. orientalis is a relatively slowgrowing species with a relatively long-life span compared to other fish.

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We would like to thank S. Karimi, M. Pourmohammad, and S. Asadolla for their assistance in the laboratory. This study was financially supported by Isfahan University of Technology.