2.1. Determination of LC50 Values

Milkfish, Chanos chanos, (weight 16 ± 1 g and length 11 ± 1 cm) were collected from Agniar estuary (Lat. 10°20′ N; Long. 79°23′ E) near Adirampattinam, southeast coast of India. The fishes were stocked in large cement tanks, washed and sterilized with potassium permanganate solution. Experimental fishes were maintained in small plastic troughs (20 L capacity). Physico-chemical parameters of tank water during trial conditions included: temperature: 24.5 ± 0.5 °C; pH: 8.3 ± 0.26; salinity: 17.0 ± 1.15 ppt; dissolved oxygen: 5.24 ± 0.1 mg/L. The water was changed frequently from the tanks set up in the laboratory in order to ease the burden of fish being sensitive to ammonia build up. Sodium Arsenite (Na₂AsO₂) purchased from (Loba Chemie Pvt Ltd., Mumbai, India) was used in the present study. Bioassay tests were carried out for the determination of LC₅₀ values for 96 h in accordance with the methodology of [4] where, different concentrations of arsenic (1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 ppm) were prepared from the stock solution (1 ppt) enlisted in the Table 1. A set of ten fishes in triplicates, were introduced into the segregated experimental concentrations. Physico-chemical parameters of tank water during experimental conditions included: temperature: 24.5 + 0.5 °C; pH: 8.4 ± 0.21; salinity: 17.0 ± 1.15 ppt; dissolved oxygen: 5.16 ± 0.1 mg/L. Following exposure, fishes were randomly selected after 30 days where studies on oxygen consumption, hematological and histological changes were carried out with an interval period of 10 days.

Percent mortality of Chanos chanos exposed to different concentrations of arsenic for different periods (ppm).

Abbreviations and notations: LC₅₀—lethal concentration required to kill 50% of the population; UCL—upper confidence limit; LCL—lower confidence limit (present study recorded 95% confidence levels, which is ideal).