In recent years there has been a growing interest in the study of hematological and biochemical parameters of fish blood, regarded as important for aquaculture purposes. The study of blood characters can corroborate the diagnoses and prognoses of morbid conditions in fish populations (Tavares-Dias and Moraes, 2004) and thereby contribute to better comprehension of the comparative physiology, phylogenetic relations, feeding conditions and other ecological parameters. Baseline data regarding hematological and plasma biochemical reference values facilitates the fish health condition assessment of diagnostics in freshwater fish (Pradhan et al., 2012b). There are abundant and excellent references for guidance regarding abnormal fish health, and the incisive expert needs to use all available diagnostic skills to manage these cases whereby the use of clinical pathology is a great enhancement for this challenge. Once reference values are determined in L. rohita, they can facilitate monitoring of the fish stress response, their nutritional condition, reproductive state, tissue damage due to frequent handling procedures, detection, and diagnosis of metabolic disturbances or disease processes in the fish population (Congleton and Wagner, 2006). Many hematological reports are available for small and young Cyprinidae fishes by different researchers using various approaches; the present work basically focused on reference ranges for hematological and plasma biochemical parameters in adult species of L. rohita. Our hematological data showed marginal differences in comparison with Clarias isheriensis (Kori-Siakpere, 1985) and Clarias gariepinus (Oluyemi et al., 2008), and some Cyprinidae species such as Catla catla (Pradhan et al., 2012a) and Cirrhinus mrigala (Pradhan et al., 2012b). Many publications demonstrated that variations in blood index values are attributable to factors such as age, fish size, nutritional state, season, spawning, sex, and genetic variation in different fish species. The present study findings on hematological parameters in L. rohita show statistical differences in seasonal and sex variations. Moreover, this study further attributes that because of a high body metabolic rate during summer, the high ambient temperature and reproductive activities, most of the hematological parameters showed higher values than in other seasons. The lowest value, on the other hand, was during winter, which might be because of the low ambient temperature and low metabolic rate. These findings are supported by our own research and by other researchers in other species (Orun et al., 2003; Adebayo et al., 2007). Numerous publications demonstrated that variation in hematocrit value and other hematological parameters between sexes and their diversity might be due to the higher metabolic rates of male fish. Findings in the present work also support this idea, which is related to an increase in fish activity with an increase in size. Considering the sex variations, many studies demonstrated that the male fish has higher values in almost all hematological parameters except in TLC (Orun et al., 2003). These higher values favouring males may be attributed to their physiological activeness. During our 2-year study, MCHC and MCH values did not show any marked differences between seasons and sexes. In freshwater fish, the blood glucose level may vary due to different external as well as internal factors, including diet. Declines in glucose levels during winter probably reflect the reduced feed intake in comparison to spring and summer as well as the increase in tissue uptake that is mediated by pancreatic hormones (Sheridan and Mommsen, 1991). Previous studies by various researchers demonstrated that basal levels of glucose varied in ecologically-distinct species, in part influenced by environmental and non-environmental factors such as feeding habits and life mode of the fish, particularly related to locomotion (Tavares-Dias and Moraes, 2004). In the present L. rohita study, the plasma glucose values were lower in autumn and winter, but higher in spring and summer. Similarly, total protein in these fishes varied slightly throughout the year in males compared to females, with higher values in winter and spring. Our results corroborate the reports of Hrubec et al. (2001) and our earlier reports in two other carp species (Pradhan et al., 2012a,b). The decrease in protein content in the summer may be due to augmented proteolysis and possible utilization of the product for metabolic purposes and/or utilization in the development of gonads. Many publications demonstrated that the seasonal fluctuations of lipids might be controlled by an endogenous biological clock, which exerts an independent effect on fish blood; they reported that the comparative increase in lipid during summer might be due to the demands of energy and environmental alterations, which enhance metabolic stress that reduces the metabolic reserves. In female fish, the cholesterol level is highest in the summer and lowest in the winter, which may be due to reproductive activity.
In conclusion, this study has established a reference value regarding the selected hematological and plasma biochemical parameters of L. rohita, similar to the reference values for the other tropical freshwater species, C. catla and C. mrigala. Establishment of hematological and plasma biochemical parameters is highly dependent on endo- and exogenous factors, including living conditions, season, age, gender, origin, breeding system, physiological and nutritional status, and genetics of each individual that governs reference values for fish, which can be useful in many fields. Although most wild fishes in a freshwater pond were sampled, the small numbers of any specific fish population limits the interpretation of the results, thus further validation is required. In summation, there is an urgent need for a reliable database for this economically important species.