Effect of Environmental Factors on Chrysochromulina Growth; the Most Common Cause of Fish Mortality in Jeddah Download PDF

A phytoplankton bloom, dominated by the prymnesiophyte Chrysochromulina sp., developed in two areas of the red sea coast, Al-Nawras and Al-Arbaeen lagoons (Jeddah, Saudi Arabia) in the fall of October and December 2016. Chrysochromulina sp. dominated at total cell densities of average 3×10⁶ cells.ml^-1, and have caused variable degrees of mortality in fish. Fish gills were examined under a microscope and showed the presence of Chrysochromulina sp cells. This study was conducted to investigate environmental factors that affect the growth characters as a function of different salinity, pH, temperature, and light-regime (light duration and intensity). Light-regime showed the highest effect among all the factors tested, at 10:14h L:D for the light duration with a growth rate of (0.352 μ.d^-1), dry weight of (1552.601 ng), production per dry weight of (542.613 ng.d^-1), and chlorophyll-a content (0.221µg.ml^-1), as for light intensity, the best results were at around 60 to 70 µmol with a growth rate of (0.426 μ.d^-1), dry weight of (2213.086 ng), production per dry weight of (929.419 ng.d^-1), and chlorophyll-a content of (0.205 µg.ml^-1). Other factors were best at 15°C, 40 PSU, and 7 to 8 for the temperature, salinity, and pH, respectively. No acute toxicity was present. Therefore, the fish mortality was most likely related to the morphological aspect of the isolated species by clogging of fish gills accompanied with suitable environmental conditions, grazing and a very low dissolved oxygen level in both lagoons.