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Periophthalmodon septemradiatus (Hamilton, 1822) is a unique mudskipper living in the mudbanks from estuarine to riverine regions in the Vietnamese Mekong Delta (VMD), but there is no data on its growth patterns and condition factors that are helpful for fish resource assessment and adaptation understanding. This study was conducted at five sites, from the lower (Soc Trang province) to middle (Can Tho city) and upper (An Giang province) reaches of Bassac River in VMD, to provide knowledge on growth patterns and condition factors to this mudskippers. Fish samples were caught using traps and hands for 24 months, from July 2017 to June 2019, at these five sites. The total length and weight of 3,417 individuals (1,340 females and 2,077 males) varied by sex, season and site (p < 0.001 for all cases). This species exhibited a positive allometric type as the slope (b = 3.06 ± 0.01) of the length-weight relationship (LWR) was >3 (p < 0.001) for both sexes. The growth pattern changed with sex as mudskipper showed isometry in females but positive allometry in males. Maturity also affected fish growth type since it shifted from negative allometry in immature groups to positive allometry in mature groups. The growth pattern of fish changed from isometry in the dry season to positive allometry in the wet season. The mudskipper showed isometry at the lower reaches in Soc Trang but positive allometry at the middle and upper reaches in Can Tho and An Giang. The condition factor (CF) did not change according to sex, size and season, but with month and site variables. The present environmental condition in these studied sites tended to be not good enough for this fish as CF (0.95 ± 0.01) was less than 1 (p < 0.001). The findings provided basic information on the growth and adaptation of P. septemradiatus being helpful in fish adaptation understanding and resource conservation in VMD. [ABSTRACT FROM AUTHOR]

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 D 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present study was conducted in four sampling sites, from fresh to brackish waters, to contribute knowledge on the length-weight relationship, growth, and body condition factor of the commercial fish Glossogobius aureus (Gobiiformes: Gobiidae) in the Mekong Delta. Fish specimens were caught using gill nets from January to December 2020. Data analyzed results of 742 specimens (382 males and 360 females) showed that weights of males and females in various sizes, seasons, and sites are able to estimate from a fish given length due to high determination coefficients (r²> 0.8, in all cases). The growth pattern of Glossogobius aureus fluctuated monthly from negative allometry to isometry and positive allometry as its slope (b) obtained from LWRs ranged from 2.583±0.119 SE to 3.123±0.066 SE. Likewise, b of this fish changes with fish size and site, but not season and gender. Albeit the growth pattern showed intraspecific and spatio-temporal variations, this goby displayed negative allometry since b (2.859±0.030) was lower than three. Likely, fish body condition factors, ranging from 0.937±0.022 SE to 1.218±0.030 SE, varied between fish sizes, sites, and months. The present findings contributed valuable data to understand fish adaptation and fishery management. [ABSTRACT FROM AUTHOR]