Profile of ectoparasites and biometric condition of snakehead (Channa striata Bloch 1793) collected from different habitats

Studies related to the comparison of ectoparasites that infect snakehead from different habitats and their relationship to biometric conditions have not been widely studied. Thus, present study aimed to investigate the prevalence, intensity, dominance, and predilection of ectoparasites on snakehead collected from ditches, paddy fields, and swamps and correlate them with biometric conditions. In total of 90 snakehead fish were collected from ditches, paddy fields, and swamps. The observation of ectoparasites was performed on the gills, fins, and skin. The parameters measured in this study were ectoparasite profiles and biometric condition of fish. Specifically, the parameters of the ectoparasite profile included prevalence, intensity, dominance, and predilection. Meanwhile, the parameters of the biometric conditions were the length-weight relationship, the distribution of length and weight classes, and condition factors. Five species of ectoparasites that have been identified as Tetrahymena sp., Epistylis sp., Trichodina sp., Dactylogyrus sp., and Gyrodactylus sp. Tetrahymena sp. infection in snakehead was reported for the first time. The ditch habitat had the highest prevalence and intensity, which were 76.7% and 15.4 ectoparasites/fish, respectively. Tetrahymena sp. and Epistylis sp. were detected in sneakhead from all habitats, Trichodina sp. was detected at ditch and paddy field habitats, whereas, Gyrodactylus sp. and Dactylogyrus sp. were only found in swamp habitats. The gill was the predilection organ that most vulnerable to ectoparasite infection. Infected Snakehead tend to have lower average weight and length than healthy snakehead. Snakehead with a weight range of 115.2-145.2 g and a length range of 258.5-268.5 mm tend to be more vulnerable to ectoparasite infection compared to other sizes.Keywords:Tetrahymena sp.PrevalenceIntensityPredilectionLength-weight relationship

Estimation of Groundwater Recharge in Kumamoto Area, Japan in 2016 by Mapping Land Cover Using GIS Data and SPOT 6/7 Satellite Images

Agricultural fields, grasslands, and forests are very important areas for groundwater recharge. However, these types of land cover in the Kumamoto area, Japan, were damaged by the Kumamoto earthquake and heavy rains in 2016. In this region, where groundwater provides almost 100% of the domestic water supply for a population of about 1 million, quantitative evaluation of changes in groundwater recharge due to land cover changes induced by natural disasters is important for the sustainable use of groundwater in the future. The objective of this study was to create a land cover map and estimate the groundwater recharge in 2016. Geographic information system (GIS) data and SPOT 6/7 satellite images were used to classify the Kumamoto area into nine categories. The maximum likelihood classifier of supervised classification was applied in ENVI 5.6. Eventually, the map was cleaned up with a 21 × 21 kernel filter, which is larger than the common size of 3 × 3. The created land cover map showed good performance of the larger filter size and sufficient validity, with overall accuracy of 91.7% and a kappa coefficient of 0.88. The estimated total groundwater recharge amount reached 757.56 million m3. However, if areas of paddy field, grassland, and forest had not been reduced due to the natural disasters, it is estimated that the total groundwater recharge amount would have been 759.86 million m3, meaning a decrease of 2.30 million m3 in total. The decrease of 2.13 million m3 in the paddy fields is temporary, because the paddy fields and irrigation channels have been improved and the recharge amount will recover. On the other hand, since the topsoil on the landslide scars will not recover easily in natural conditions, it is expected to take at least 100 years for the groundwater recharge to return to its original state. The recharge amount was estimated to decrease by 0.17 million m3 due to landslides. This amount is quite small compared to the total recharge amount. However, since the reduced recharge amount accounts for the annual water consumption for 1362 people, and 12.1% of the recharge decrease of 1.41 million m3 each year to fiscal year 2024 is expected by municipalities, we conclude that efforts should be made to compensate for the reduced amount due to the disasters.