Aquacultura Indonesiana (2014) 15 (2): 86-93 ISSN 2477- 6939 AQUACULTURA INDONESIANA An International Journal of Indonesian Aquaculture Society (www.aquasiana.org) © Copyright by the Indonesian Aquaculture Society 2014 86 Haematological, Biochemical and Clinical Signs Changes Following Experimental Infection of Streptococcus agalactiae in Red Hybrid Tilapia (Oreochromis sp.) Milud Alsaid 1 , Ali F. Abuseliana 2 , Hassan H. Daud, Noordin M. Mustapha, Siti Khairani Bejo, Yasser M. Abdelhadi, and Ruhil H. Hamdan 3 1 University of Almergeb/ Departmentof Aquatic Biology, Alkhums, Libya 2 Tripoli University, Tripoli, Libya 3 Universiti Putra Malaysia, Department of Veterinary Clinical Studies, Selangor state , Malaysia Correspondence to : maalshaafai@elmergib.edu.ly Abstract Milud Alsaid, Ali F. Abuseliana, Hassan H. Daud, Noordin M. Mustapha, Siti Khairani Bejo, Yasser M. Abdelhadi, and Ruhil H. Hamdan. 2014. Haematological, Biochemical and Clinical Signs Changes Following Experimental Infection of Streptococcus agalactiae in Red Hybrid Tilapia (Oreochromis sp.) Aquacultura Indonesiana, 15 (2) : 86-93. Hematological and biochemistry parameters are essential for the evaluation of fish health status; it helps provide essential information to diagnose fish diseases. This experiment was conducted to investigate the affect of Streptococcus agalactiae infection on hematological and biochemical parameters in red hybrid tilapia ( Oreochromis sp.). The fish were inoculated intraperitoneally with 1 x10 4 cfu/mL bacteria then blood samples were collected and tested during the experiment. After seven days The red blood cell (RBC) counts decreased from 2.31 x 10 6 to 1.68 x 10 6 . The hemoglobin (Hb) and hematocrit (PCV) counts decreased to 7.17 g/dL and 19.2% in the infected fish compared to the control group (9.71 g/dL and 28.20%). In contrast, the white blood cell (WBC) counts increased from 4.20x10 3 in the control fish to 13.2x10 3 . The biochemical results initially showed an increase in glucose levels of the infected fish compared to the control from 53.82 to 101.75 on the 72 nd hour, respectively. There were no significant differences in the levels of serum total protein (T. prot), albumin (ALB), and aspartate transminase (AST) between the infected and the control fish. The inoculated fish displayed marked clinical signs such as erratic swimming behavior, exophthalmia and lethargy during the experimental. The present study has established that the changes in hematological, biochemical and clinical signs of fish can be used as an early diagnosis of pathological and physiological status in red tilapia culture. Keywords: Biochemical; Clinical signs; Hematological; Oreochromis sp.; Streptococcus agalactiae Introduction Red hybrid tilapia (Oreochromis sp.) is becoming very important commercial venture as they are well accepted by people, it grow fast and has rapid weight gain. Tilapia most widely cultured in ponds, cages and tanks as well as in pen culture systems (Hamzah et al., 2008). The first introduction of red hybrid tilapia O. niloticus to Malaysia was in the mid 1980s. Since their introduction, red tilapia production has increased significantly (Siti-Zahrah et al., 2008). Currently, tilapia is a commonly aquacultured fish and it is an important seafood source for human consumption. Up to date, still little is known about their normal physiology and responses to disease infection. Hence, continuous improvement in the health assessment methods of tilapia is an essential. However, hematology which is frequently used for diagnostic clinical diseases in veterinary world, the techniques are still limited in aquatic animal health medicine (Chen et al., 2003). One of the most significant emerging diseases in tilapia farming in the Asia- Pacific region and particularly in closed systems is caused by Streptococcus sp. bacteria. Streptococcosis is caused by Streptococcus agalactiae (S. agalactiae), which infects both animals and humans causing meningoencephalitis in fish, mastitis in cows, and neonatal sepsis in humans (Pereira et al., 2010). This bacterium affects most of the marine and fresh water fish, including Gulf killifish (Fundulus grandis) (Rasheed and Plumb, 1984), red hybrid tilapia (O. aureus and O. niloticus). Eldar et al. (1995), sea bream Sparus auratus Evans et al. (2002) and silver pomfret (Pampus argenteus) Duremdez et al. (2004) Streptococcosis in tilapia is the most considered destructive bacterial disease. It is usually caused by S. agalactiae Pasnik et al. (2009) leading to an acute or chronic, systemic disease with high morbidity and mortality. In May 2010, mass mortality in red hybrid tilapia occurred on a farm in Selangor state, Malaysia. In an earlier report the mortality was determined to be associated with