Spatiotemporal variations in length-weight relationship, growth pattern and condition factor of Periophthalmus variabilis Eggert, 1935 in Vietnamese Mekong Delta

Abstract

Length-weight relationship (LWR), growth pattern and condition factor (CF) play a vital role in fish resource evaluation and management but data on this is limited for Periophthalmus variabilis. This is an amphibious fish that lives in the mudflats of the mangrove forests in the Western Pacific regions, including the Vietnamese Mekong Delta (VMD). This paper contributes to the understanding of the LWR, growth pattern and CF of P. variabilis. Fish specimens were collected by hand at four sites in the VMD from April 2020 to March 2021. The analysis of 495 individual fish (259 females and 236 males) showed that fish weight could be estimated from a given fish length due to high determination values (r2 = 0.70 − 0.97). Dusky-gilled mudskippers of the VMD exhibited positive allometry, as indicated by their larger than 3 b value (b = 3.094 ± 0.045, p = 0.04). However, the growth pattern of the mudskipper between the sex and maturation stage (immature versus mature) showed isometry. These fish displayed positive allometry in the dry season (b = 3.138 ± 0.065) (>3, p = 0.04) but isometry in the wet season (b = 3.058 ± 0.061) (≈3, p = 0.34). Fish growth ranged from isometry to positive allometry and varied by site (b = 2.850 ± 0.103–3.370 ± 0.114) and month (b = 2.668 ± 0.184–3.588 ± 0.299) based on the b value. The CF of P. variabilis was not affected by sex (p = 0.29), body size (p = 0.64) or season (p = 0.43), but was affected by site (p = 0.01) and month (p = 0.01). The CF of this species (1.05 ± 0.02) was higher than 1 (p < 0.001), indicating that the fish adapted well to their habitat.

Factors regulating growth pattern and condition factor of an amphibious fish Periophthalmus gracilis living in the Mekong Delta

“…Likewise, its congeners living out of MD was also adapted well to their habitats due to higher CF , e.g. , P. barbarus ( King & Udo, 1998 ), P. chrysospilos ( Abdullah & Zain, 2019 ; Dinh et al, In Press ), P. modestus ( Tran, Nguyen & Ha, 2021b ) and P. variabilis ( Dinh et al, 2022 ). This assumption was also found in some other fish species in MD, such as P. elongatus ( Tran, 2008 ), P. serperaster ( Dinh et al, 2016 ), T. vagina ( Dinh, 2016b ), P. schlosseri ( Dinh, 2016c ) and G. aureus ( Dinh, 2019 ) and G. giuris ( Phan et al, 2021b ).…”

Monthly variations in growth pattern and condition factor of Periophthalmodon septemradiatus (Gobiiformes: Periophthalminae) living along the Bassac River in Viet Nam

“…The species P. septemradiatus displayed a temporal change in growth type, shifting from isometry to positive allometry. This assumption was also found in P. schlosseri ( Dinh, 2016 ), P. chrysospilos ( Dinh et al, 2022d ), P. variabilis ( Dinh et al, 2022b ), and P. gracilis ( Dinh et al, 2022c ).…”

“…The mudskipper P. septemradiatus exhibited high correlation between TL and W ( r 2 = 0.92–0.98), indicating that W was estimated from a fish given length. Some other mudskippers living in and out of the VMD also demonstrated a high correlation in LWRs, e.g ., B. boddarti in VMD and India ( Dinh, 2017b ; Mahadevan & Ravi, 2018 ), P. novemradiatus in India ( Mahadevan & Ravi, 2018 ), P. variabilis in VMD ( Dinh et al, 2022b ) and P. gracilis in VMD ( Dinh et al, 2022c ). The high correlation in LWRs was also found in some other gobies in the VMD, e.g ., Glossogobius sparsipapillus ( Dinh, 2015 ; Truong et al, 2021 ), Butis butis ( Dinh, 2017a ) and G. giuris ( Dinh & Ly, 2014 ; Phan et al, 2021b ).…”

“…By contrast, P. schlosseri a congener of P. septemradiatus living in the mudflats on the coastline of VND showed an isometry ( b = 2.96) ( Dinh, 2016 ). Besides, some other mudskippers distributed mudflats in the estuarine and coastal regions like P. variabilis in VMD ( Dinh et al, 2022b ), P. waltoni in Sourgalm, Iran ( b = 3.00) ( Ghanbarifardi et al, 2014 ), B. boddarti ( b = 3.00) ( Khaironizam & Norma-Rashid, 2002 ) also displayed isometry. Some other mudskipper exhibited negative allometry, e.g ., P. gracilis in VMD ( b = 2.69) ( Dinh et al, 2022c ), P. waltoni in Mahshahr, Iran ( b = 2.82) ( Ghanbarifardi et al, 2014 ), P. novemradiatus ( b = 2.67), S. histophorus ( b = 2.62) in Malaysia ( Khaironizam & Norma-Rashid, 2002 ).…”

“…The regression parameters as the intercept (initial growth coefficient) and the slope (growth coefficient) of the LWR are helpful to determine the growth pattern of fish ( Froese, 2006 ). The growth pattern can change with sexes, fish sizes, seasons and sites ( Froese, Palomares & Pauly, 2000 ; Dinh et al, 2022a ). Condition factor (CF) is an essential factor in the study of fish adaptation to the environment ( Abdoli et al, 2009 ; Dinh, 2016 ).…”