In Uzbekistan, all river basins are endorheic; therefore, fish diversity is poorer than in other regions. One-quarter of the fish species in the country are endemic (Mirabdullaev and Mullabaev 2020). The recent discovery of two species of Triplophysa Rendahl, 1933 from the upper reaches of the Syr Darya also confirms this statement (Sheraliev and Peng 2021; Sheraliev et al. 2022). The majority of endemic and indigenous fish species from the inland waters of Uzbekistan do not have commercial value but are important for aquatic ecosystems (Mirabdullaev and Mullabaev 2020; Sheraliev and Peng 2021; Sideleva 2021).

A prerequisite in assessing the population characteristics of any fish species is to investigate its length–weight relation (LWR) (Le Cren 1951). LWRs provide basic knowledge for fisheries research, which is important for fish management and conservation (Çiçek et al. 2022). A few commercially important fish species in Uzbekistan have available LWR data (Kurbanov and Kamilov 2015; Kamilov et al. 2017; Sheraliev et al. 2019); however, no such studies on non-commercial endemic fish species have been undertaken. Because of this scarcity of information, the presently reported study was carried out to determine the LWR parameters of 12 endemic and two native fish species inhabiting the Aral Sea basin in Uzbekistan.

A total of 676 individuals representing 14 endemic and native fish species were collected between March 2020 and June 2022 from the Syr Darya, Amu Darya, and Zeravshan rivers and their various tributaries using hand nets (Table 1). The following species were collected: Holcik’s riffle minnow, Alburnoides holciki Coad et Bogutskaya, 2012; sharpray, Capoetobrama kuschakewitschi (Kessler, 1872); Turkestan sculpin, Cottus spinulosus Kessler, 1872; Oshanin’s catfish, Glyptosternon oschanini (Herzenstein, 1889); Turkestan gudgeon, Gobio lepidolaemus Kessler, 1872; Hari gudgeon, Gobio nigrescens (Keyserling, 1861); Kuschakewitsch loach, Iskandaria kuschakewitschi (Herzenstein, 1890); Tajik loach, Iskandaria pardalis (Turdakov, 1941); eastern crested loach, Paracobitis longicauda (Kessler, 1872); Aral spined loach, Sabanejewia aralensis (Kessler, 1877); Zeravshan marinka, Schizothorax fedtschenkoi Kessler, 1872; Sokh stone loach, Triplophysa daryoae Sheraliev, Kayumova et Peng, 2022; Fergana stone loach, Triplophysa ferganaensis Sheraliev et Peng, 2021; and Zeravshan stone loach, Triplophysa uranoscopus (Kessler, 1872). The specimens collected were identified with the aid of Berg (1949), Turdakov (1963), Amanov (1985), Thoni et al. (2017), and Sheraliev and Peng (2021) as representing three orders, seven families, and ten genera (Fig. 1). The fishes were measured to the nearest 0.1 cm total length (TL) using a digital caliper and weighed to the nearest 0.01 g total weight (W). LWRs were calculated using the following equation

W = aTL^b

and logarithmically transformed (Froese 2006) into

Log (W) = log(a) + b ∙ log(TL)

where W is the total body weight [g], TL is the total body length [cm], a is the intercept, and b is the slope. The 95% confidence limits of a and b, and the coefficient of determination (r²) were calculated using the equations of Sparre and Venema (1998). All statistical analyses were performed using MS Excel 2019 software.

For all collected species, the coefficient of determination (r²) ranged from 0.951 to 0.993, the a value ranged from 0.0046 to 0.0132, and the b values ranged from 2.703 to 3.234. Sample sizes, total length and total weight ranges, regression parameters, 95% confidence limits of a and b values, and coefficients of regression are given in Table 2. In LWRs, b values higher and lower than 3 indicate positive and negative allometric growth, respectively. According to their b values, Iskandaria pardalis, Schizothorax fedtschenkoi, Glyptosternon oschanini, Triplophysa uranoscopus, Sabanejewia aralensis, Cottus spinulosus, and Capoetobrama kuschakewitschi are isometric; Iskandaria kuschakewitschi, Paracobitis longicauda, and Triplophysa daryoae have negative allometry; and Alburnoides holciki, Gobio lepidolaemus, Gobio nigrescens, and Triplophysa ferganaensis have positive allometry (Table 2). The new maximum total lengths of Glyptosternon oschanini, Iskandaria kuschakewitschi, Triplophysa daryoae, and Triplophysa uranoscopus were updated.

Overall, the expected range of b values for LWRs is 2.5–3.5 (Froese 2006) although the ideal value of b is 3.0 (Le Cren 1951). The results of the presently reported study are concordant with the expected range. It has been shown that when b is greater than three, fish grow faster in weight than in length (Islam et al. 2017; Yang et al. 2021). In addition, a b value lower than 3.0 signifies that fish expend more energy on axial growth than to accumulate mass, which could help them seek food and avoid predators (Yang et al. 2021). The calculations performed in this study indicate that, in Iskandaria kuschakewitschi, Paracobitis longicauda, and Triplophysa daryoae, parameter b was lower than 3.0, which may be due to cold water, severe environment, low availability of food resources, the large abundance of predators and food competitors, and other unpredictable reasons (Le Cren 1951; Rypel and Richter 2008; Wang et al. 2016). On the other hand, several scientific results indicate that the b value of the same species can vary depending on several factors, including environmental factors such as habitat type, seasonality, and geographic location; biotic factors such as sex, gonadal maturity, health, degree of stomach fullness, food competition, and trophic potential of rivers or ponds; and anthropogenic factors such as gear selectivity, number of examined specimens, and a length range of observed individuals (Hossain et al. 2006; Siddik et al. 2016; Islam et al. 2017; Sheraliev et al. 2019). In previous studies, the maximum lengths of Glyptosternon oschanini, Iskandaria kuschakewitschi, Triplophysa daryoae, and Triplophysa uranoscopus were given as 10.4, 11.0, 11.2, and 9.0 cm, respectively (Thoni et al. 2017; Froese and Pauly 2022; Sheraliev et al. 2022). By examining a different subsample in the presently reported study, these records were revised to 17.6, 14.6, 11.3, and 11.5 cm, respectively.

In conclusion, our study provides partial information on the 14 endemic and native fish species from the Aral Sea basin as a contribution to the online FishBase, which could help to understand better the fishes of the region and contribute to the management and conservation of fishes in central Asia.