Search

Length-weight relationship (LWR) was used as a tool to assess the status of fish stocks, through condition factor, in major rivers in Thailand. Fifty-one fish species from each river, i.e., The examined for LWR using 11 years of monitoring data (2010–2020) for Bang Pakong and 14 years of monitoring data (2007–2020) for Chao Phraya, which comprised 57,871 samples. The parameters for LWR and condition factor were examined by species and by body shape, i.e., ovate, oblong, elongate or eel-like. The coefficient of determination (r²) of all log-transformed LWRs was greater than 0.90. Parameter b of LWR ranged between 2.06 and 3.46 (median = 3.00) for fishes from the Chao Phraya River and between 1.72 and 3.68 (median = 2.76) for fishes from the Bang Pakong River. The overall condition factor, which implies the well-being that indicates the health or fattening of the fishes in a stock, ranged between 0.93 and 1.09. There was no significant difference in the overall well-being (P = 0.279) between the two rivers. Fishes with oblong and elongate shapes in the Chao Phraya River showed higher median values of parameter b of LWR than those from the Bang Pakong River. However, there was no significant difference (P > 0.05) in the well-being of the fish stocks between the two rivers when pooled by shape. The findings are fundamental information for fish stock assessment in the two rivers, which greatly support the small-scale fisheries in Thailand. [ABSTRACT FROM AUTHOR]

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]

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409–0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed. [ABSTRACT FROM AUTHOR]