M.N.A  Amal, M.  Zamri-Saad, A.R.  Zulkafli, A.  Siti-Zahrah, S.  Misri, B.  Ramley, H.  Shahidan, M.Y.  Sabri, 
    Water Thermocline Confirms Susceptibility of Tilapia Cultured in Lakes to <I>Streptococcus agalactiae</I>,
    Journal of Animal and Veterinary Advances,
    Volume 9,Issue 22,
    2010,
    Pages 2811-2817,
    ISSN 1680-5593,
    javaa.2010.2811.2817,
    (https://makhillpublications.co/view-article.php?doi=javaa.2010.2811.2817)
    Abstract: A study was conducted on water quality profiling to confirm susceptibility of tilapia cultured in lakes to <I>Streptococcus agalactiae</I> infection. A total of 1,010 and 719 tilapias of different sizes were collected from two lakes; the Kenyir and Pedu lakes, respectively. They were randomly sampled for a period of 24 months. Swabs of brain, eye and kidney were streaked directly onto blood agar before <I>S. agalactiae </I>was identified by the API 20 STREP kit, Slidex Strepto-kit and PCR technique. The water temperature (thermocline) and dissolved oxygen profiling were determined at 1 m intervals for up to 20 m deep. Water clarity and flow rate were also recorded using Secchi disk and a current meter. <I>S. agalactiae</I> was successfully isolated from both lakes throughout the year, ranging between 2 and 78%. Isolation was more frequent during the hot and dry months of both years. During this period, the mean water temperature was &gt;29&deg;C for up to 8 m deep due to the significantly (p&lt;0.05) clearer water and slow rate of water flow that allowed deeper light penetration and enhanced heat retention. Water thermocline that showed a drop in water temperature was observed only in Kenyir lake at &gt;12 m deep. This and the slow water flow kept the water temperature at 4 m deep where tilapias under the cage culture system were kept to remain high causing stress to tilapia and increases susceptibility to <I>S. agalactiae. </I>Dissolved oxygen profiling, however remained high at &gt;5 mg L<SUP>-1</SUP> for up to 8 m deep and did not give adverse effects to susceptibility of tilapia to <I>S. agalactiae</I>.
    Keywords: Water profiling;lakes;tilapia;Streptococcus agalactiae;temperature;Secchi disk