Condition Factor (CF), Hepatosomatic Index (HSI) and Gonadosomatic Index (GSI) of fish
Analyses of CF, HSI and GSI of fish could offer information on the general health condition of the organisms
Pollution may damage organisms directly by increasing their mortality, or interfering with the processes of food acquisition and uptake, and reducing their growth and reproduction rates. Growth represents the integration of feeding, assimilation and energy expenditure over a period of time. Poor growth means less energy is available for reproduction, which will in turn reduce the species fitness and lead to a decline in population. Growth and reproduction therefore can serve as a time-integrated indicator of the general well being of the organism.
Condition Factor (CF) calculated by weight/body length has been used to compare growth conditions of fish. A high condition factor reflects good environmental quality; while a low condition factor reflects poor environmental quality. Hepatosomatic Index (HSI) is defined as the ratio of liver weight to body weight. It provides an indication on status of energy reserve in an animal. In a poor environment, fish usually have a smaller liver (with less energy reserved in the liver). HSI has been reported to decrease in fish exposed to high concentrations of cadmium and zinc. Gonado-Somatic Index (GSI) is the ratio of gonad weight to body weight used to estimate reproductive condition. Reproduction is the most critical stage in the life cycle of a species, which determines its survival. GSI is generally indicative of reproductive success (and general water quality). CF, HSI and GSI are not only responsive to pollution, they can be affected by other factors such as temperature and food availability.
A total of 2098 rabbit fish Siganus oramin and, 457 pony fish Leiognathus brevirostris were examined in 2004 and 2005. Spatial gradients of CF, HSI and GSI of the target fish have been observed and the lower values (indicating poorer environmental quality) were generally recorded in Zone 4 in Port Shelter & Outer Mirs Bay. This was probably related to factors other than pollution.
Table: CF, HSI and GSI of the two fish species