Variation in water temperature and its effects on fish biology and aquatic habitat

This study investigated the effects of water temperature on fish biology and aquatic habitat. The main objective of Chapter 2 and Chapter 3 were to study the effects of water temperature of aquatic habitats in the Chao Phraya River and three reservoirs in North-East Thailand, Ubol Ratana, Huay Luang, and Sirindhorn. The main object of Chapter 4 was to study the effects of water temperature on fish biology. Henicorhychus siamensis was selected as the representative fish in this study. Spatio-temporal variations in the water quality of the Chao Phraya River were examined on an average yearly basis from 1999 to 2008 at 32 surface water stations from the river’s origin to its delta. Five water quality parameters, dissolved oxygen, biochemical oxygen demand, total coliform bacteria, fecal coliform bacteria, and ammonia, were used in the analysis. Analysis was performed by the use of Self Organizing Maps and correspondence analysis. Meanwhile, seasonal variations of primary production, water temperature, pH, dissolved oxygen, total phosphorus, total nitrogen, dissolved inorganic carbon, and chlorophyll a were conducted in the three reservoirs from May 2012 to February 2013. The sampling stations were located in the deepest areas and water samples were collected at different levels of the water column dependent on the percentage of photo-synthetically active radiation at 100%, 50%, 20%, 10%, and 5% respectively. The samples in the water column were analyzed and compared with the seasonal variations for both periods and reservoirs. The last chapter studies the effects of temperature, an important environmental factor for aquatic animals, especially fishes, particularly during the early stages of life. The study of embryo development and hatching success was done at different water temperatures (26, 28, 30, 32 and 34 ํC) while acute temperature change was investigated with newly-hatched larvae. The results of spatio-temporal variations in the water quality of the Chao Phraya River indicated four distinct spatially approached clusters according to the similarity of the water quality parameters, while temporal variations at most of the surface water stations were not obviously observed. The worst water quality condition was at the stations near the river delta and highly related to anthropogenic stresses. While results from the correspondence analysis showed that, except for the cluster of the worst water quality, the stations of the remaining three clusters overlapped. There was no statistical difference in water temperatures among clusters but the expected effects from climate change should be a precautionary focus since they will eventually affect the water quality. The seasonal variations of primary production influenced primary production and another variable. Thermal stratifications were observed in all reservoirs, especially Sirindhorn that thermoclines were obvious in February. Meanwhile, primary productions were significantly different among the PAR levels in all four periods of the study. Comparison of the three reservoirs showed that Huay Luang had the highest primary production. These finding’s demonstrated the usefulness of aquatic habitat management and conservation. Meanwhile, the egg development was divided into two phases, firstly, from zygote to gastrula periods and secondly, segmentation to hatching periods. The larvae did not successfully hatch at the incubation temperatures of 26 and 34 ํC. The development times of the three remaining temperatures were relatively close in the first phase, in contrast to the second phase which was more varied. The hatching times at 28, 30 and 32 ํC were about 652, 485 and 457 minutes respectively. The percentages of hatching success of the three respective temperatures were 73.76+-2.37%, 73.90+-1.44% and 61.42+-11.19% respectively. In regard to the effects of acute temperature changes, numbers of dead larvae were not significantly different between 30 ํC and 28 ํC (P=0.30). There was a significant difference between 30 ํC and 32 ํC (P<0.01).