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

Abstract

Growth pattern and condition factor (CF) are essential to fish resource assessment but limited to Periophthalmus gracilis—an amphibious fish living in the mudflats along the Indo-Pacific regions, including the Mekong Delta (MD), Vietnam. This study lasted from April 2020 to March 2021 to verify if their growth pattern and CF change with sex, size, season, month and site. The total length and weight of 486 individuals (236 females and 250 males) were 2.9–5.9 cm and 0.13–1.66 g, respectively. The mudskipper displayed negative allometry as the slope value (b = 2.69 ± 0.06) obtained from length and weight (LWR) was significantly less than 3 (p < 0.01), indicating that most fish specimens were caught in the immature stage. The fish growth pattern did not change with sex as both males and females displayed negative allometry but varied by size since the mudskipper showed negative allometry in the immature group and isometry in the mature group. Likewise, growth type changed with season since fish showed negative allometry in the dry season but isometry in the wet season. As the slope value (b) varied by site and month, the mudskipper displayed spatiotemporal growth patterns, ranging from negative to positive allometry. The CF was impacted by sex as this value of females (1.09 ± 0.02) was higher than that of males (0.96 ± 0.01, p < 0.01). Besides, CF was regulated by fish length since this value was higher in the mature group (1.12 ± 0.03) than in the immature group (1.01 ± 0.01, p < 0.01). Likewise, CF was affected by season as this value was higher in the wet season (1.05 ± 0.02) than in the dry season (0.99 ± 0.01, p < 0.01). Although the CF varied with site and month variables (p < 0.01), this value (1.02 ± 0.01) was generally higher than 1, showing fish adapted well to their habitat. The fish length at first capture should be increased to exploit this species sustainably.

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

“…The variation in abiotic ( e.g ., salinity and mudbank slope) and biotic ( e.g ., vegetation) factors between these five sampling sites ( Dinh et al, 2021 ) could lead to the spatial change in P. septemradiatus growth pattern. This assumption was also found in P. modestus in northern Viet Nam ( Tran, Nguyen & Ha, 2021b ) and P. gracilis in VMD ( Dinh et al, 2022c ). The spatial change in growth pattern was not found in some other species of Oxudercidae like P. schlosseri ( Dinh, 2016 ) and P. chrysospilos ( Dinh et al, 2022d ).…”

“…The mudskipper growth pattern varied by sex due to the difference in the gonadal weight of males and females. The sexual change in growth pattern was found in P. modestus in northern Viet Nam ( Tran, Nguyen & Ha, 2021b ), but not P. novemradiatus in India ( Mahadevan & Ravi, 2018 ), B. boddarti in VMD and India ( Dinh, 2017b ; Mahadevan & Ravi, 2018 ) and P. gracilis in VMD ( Dinh et al, 2022c ). The species P. septemradiatus displayed intraspecific change since its growth type shifted from negative allometry in the immature fish to positive allometry in mature fish, suggesting that the energy needs increased as fish grow.…”

“…The mudskipper showed isometry in the dry season when fish consumed four types of food item types and positive allometry in the wet season when fish ingested six types of food. Likely, P. modestus in northern Viet Nam ( Tran, Nguyen & Ha, 2021b ) and P. gracilis in VMD ( Dinh et al, 2022c ) exhibited the seasonal change in growth pattern. The variation in abiotic ( e.g ., salinity and mudbank slope) and biotic ( e.g ., vegetation) factors between these five sampling sites ( Dinh et al, 2021 ) could lead to the spatial change in P. septemradiatus growth pattern.…”

“…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 ).…”

“…This assumption could be caused by the variation in food feeding and composition between these two fish groups, as Dinh et al (2020b) reported. Likewise, the growth pattern P. gracilis in VMD was also regulated by fish size ( Dinh et al, 2022c ). Males exhibited positive allometry ( b > 3), whereas females displayed an isometric pattern ( b = 3).…”