This study investigated the effects of integrating various fish species in a rice field co-culture system on water quality and soil properties. The species included common carp (Cyprinus carpio), Nile tilapia (Oreochromis niloticus), silver barb (Barbonymus gonionotus), snakeskin gourami (Trichopodus pectoralis), and giant freshwater prawn (Macrobrachium rosenbergii). The key water quality parameters measured included water temperature, dissolved oxygen, pH, transparency, ammonia, and nitrite. Soil properties were evaluated through pH, electrical conductivity, organic matter, nitrogen, phosphorus, and potassium. All the selected aquatic animals showed high adaptability in co-culture systems, with survival rates exceeding 80%. Additionally, rice yields increased by approximately 16%, with the highest yield observed in plots stocked with prawns. The results indicated that the presence of aquatic animals enhanced nutrient cycling, leading to significant improvements in both water quality and soil fertility. Differences in water quality and soil properties throughout the culture period were specific to the species present. These findings suggest that rice-fish co-culture systems serve as an effective nature-based solution for enhancing productivity, sustainability, and food security.

Understanding the proximate factors and mechanisms driving primary production in manmade reservoirs is crucial because such production can translate into added fish yields that provide people with food and livelihoods. Furthermore, reservoir fish production could potentially compensate for the loss of fish yields due to habitat fragmentation and alterations caused by damming and impoundment. We monitored primary production, identified environmental factors responsible for its variability, and examined the relationship between primary production and fish production in nine large water bodies of the Lower Mekong Basin for 2 years. The estimated primary production ranged from 40 to 302 g C/m²/y and was generally greater in the wet season than in the dry season. Linear mixed-effects modelling identified the concentration of dissolved inorganic carbon as a significant fixed-effect variable regulating primary production, after variability due to random and fixed effects of water body and seasonality, respectively, were taken into account. Fish yields marginally increased with increasing primary production across the water bodies, with the estimated energy transfer efficiency ranging from 0.004 to 0.009. Dissolved inorganic carbon was partly determined by the lithological composition of the water body catchment, suggesting that the geographic locations of proposed dams determine the magnitude of primary production and hence future fish production.

Larval fish assemblage patterns in three tributaries of Mekong River in Thailand

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 (51) fish species from each river, i.e., The examined for LWR using eleven 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.

Vulnerability of each stock in the catches from trawl fisheries in the Gulf of Thailand was assessed by productivity susceptibility analysis. Separate assessments were made based on type of trawler (otter-board, pair and beam) and vessel size (SS, S, M, L and XL, according to gross tonnage). Catches were distinctly different among trawler types and were dominated by demersal fishes, pelagic fishes and shrimps in the otter-board, pair and beam trawlers, respectively. The stocks of over 200 taxa were included in the study; high-vulnerability taxa were found for all trawl types and sizes, except the beam trawler size S. Only seven (7) taxa were classified as high vulnerability, including four (4) teleost taxa, namely Saurida elongata, Plotosus spp., Gymnothorax spp. and Sphyraena spp., and three (3) elasmobranch taxa, namely Carcharhinus spp., Brevitrygon heterura and Neotrygon kuhlii. Meanwhile, as many as 26 high-medium vulnerability taxa were found in catches by otter-board trawler size L, which included not only fishes but also cephalopods. Trends and variation in fish landings of 20 high and high-medium vulnerability taxa were analyzed. Eighteen (18) taxa showed monotonic trends, both continuous and discontinuous, in their time series of annual landings, but not Muraenesox spp. nor Uroteuthis spp. The long-term variations in fish landings ranged mostly between 40% and 50%. The short-term variations showed positive absolute and relative skewness, i.e., mostly between 10% and 20%. Results of this study highlight the taxa that require a precautionary approach for fishery management and warrant comprehensive fish stock assessment. Such data will allow more accurate determination of their status compared to the reference points and facilitate better management of trawl fisheries in the Gulf of Thailand.