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The spotted catfish, Arius maculatus (Thunberg, 1792), is a euryhaline fish that is economically important in the Indo-West Pacific. Population dynamics studies and stock assessments of this species have focused on marine stocks, but not those from fresh water. In this study, the age and growth of A. maculatus were, therefore, investigated for the inland stock in Songkhla Lake, Thailand. A total of 213 individuals ranging between 35 and 238 mm TL were used. The length--weight relation indicated positive allometry of this population. Three hard parts (otolith, dorsal- and pectoral-fin spines) were used for aging. The marginal increment ratio confirmed that an annulus was deposited once a year in all three hard parts. All of the samples were aged between 0+ and 6+ years. Verification of age estimates from three readers showed that the otolith was the most suitable part for age estimation. Three growth models (von Bertalanffy, Gompertz, and logistic) were applied in the study. The von Bertalanffy model best described the growth of this fish in Songkhla Lake. The obtained asymptotic length was 290.87 mm TL and the relative growth rate parameter was 0.166 year--1. Our results will be applied as inputs for fish stock assessment models. The obtained growth parameters also can serve as a reference for A. maculatus stocks elsewhere. [ABSTRACT FROM AUTHOR]

Fish diversity and assemblage patterns in relation to habitat characteristics were investigated in the Petchaburi River, Thailand, during the dry season and early rainy season (January to June 2019). Sampling was carried out in four stations on the river, from the upper portion downstream to the Kaeng Krachan Reservoir. A total of 5,416 individual fish were sampled from 31 species. Mean abundance was 44.6±40.1 fish per 100 m², mean species richness was 10.8±4.0, mean Shannon diversity H' index was 1.75±0.44, and mean evenness J' index was 0.32±0.05. These indices increased from upstream to downstream. They also tended to increase from the onset to middle of the dry season, then decreased at the onset of the rainy season. Co-inertia analysis indicated habitat preference in some species; for example, Tor tambroides was positively correlated with macrophytes, shade, bedrock, and boulders, whereas Aperioptus delphax preferred high velocity flows in dense vegetation, with sand and cobble substrates. The assemblage patterns were analyzed both for Q-mode (station×month) and R-mode (species) clustering, and habitat specificity of some species was clearly observed. Results of this study are timely useful for resource management and conservation, regarding that the Kaeng Krachan National Park has just been announced as UNESCO Natural World Heritage site in July 2021. [ABSTRACT FROM AUTHOR]

Age and growth of the stingray Urogymnus polylepis were determined, for the first time, from bands in the vertebrae. Samples were obtained from naturally dying specimens in the two major rivers in central Thailand. Eighteen stingrays with disc length (DL) ranging between 30 and 187 cm were collected from the Chao Phraya River, while 53 fish ranging between 30 and 250 cm were collected from the Mae Klong River. The von Bertalanffy parameters were calculated for the Chao Phraya and the Mae Klong rivers as DL∞ = 195.6 and 301.3 cm, K = 0.26 and 0.11 year-1 and DL0 = 28.1 and 27.2 cm, respectively. The likelihood ratio test showed significant difference in growth between the two populations. [ABSTRACT FROM AUTHOR]

Growth and reproduction of the Thai river sprat Clupeichthys aesarnensis (Teleostei: Clupeidae) in Sirindhorn Reservoir, Thailand, and Nam Ngum Reservoir, Laos, were investigated using age estimates obtained from daily growth increments in otoliths and gonad observations. This species breeds throughout the year in both reservoirs, although water temperature was higher in Sirindhorn than in Nam Ngum. The Sirindhorn population tended to mature at smaller size (length) and younger age than the Nam Ngum population; the Sirindhorn population also tended to grow faster before reaching sexual maturity, growing slowly afterwards, than did the Nam Ngum population. Additionally, the maximum size in the Sirindhorn population was observed to be smaller than that of the Nam Ngum population. These observations indicated that higher water temperature resulted in earlier maturation and smaller maximum size in C. aesarnensis. Meanwhile, the smaller maximum size observed in the Sirindhorn population was possibly caused by an evolutionary down-sizing resulting from the overexploitation of this population, because Sirindhorn reservoir is exposed to more intensive fishing pressure. [ABSTRACT FROM AUTHOR]

Abstract: The effect of installing an escape vent on catch and size of the mud crab Scylla olivacea (Herbst) in collapsible pots was investigated. Initially, the escape behavior of crabs was observed in a pond in the laboratory when the rectangular-shaped escape vents were located at five different positions on the pot; the aim being to determine the most suitable position for escape vents. The study also included field trials to assess the effect of different sizes of escape vents (3cm×4cm, 3cm×4.5cm, 3cm×5cm, 3cm×5.5 and 3cm×6cm) and was carried out in a commercial fishing ground in Klong Ngao mangrove swamp, Ranong Province, Thailand (latitude 9°51′ to 9°56′N and longitude 98°31′ to 98°37′E). The escape vent located at the bottom on the side panel of the pot produced the highest number of escapees. The selectivity curve of the 3cm×6cm escape vent allowed more small crabs to escape than other vent sizes. Further, the percentage of non-target species catches decreased as the size of the escape vent increased. The 3cm×6cm escape vent was the most effective for releasing undersized S. olivacea. The vents did not affect the rate of mud crab entry into the pot. [Copyright &y& Elsevier]