Abstract:
The present study was designed to evaluate the chronic exposure of iron (Fe) on the growth,
haematological and histological parameters of the Guppy (Poecilia reticulata). This experiment
was conducted with four iron concentrations (3 ppm: Fe-3, 5 ppm: Fe-5, 10 ppm: Fe-10 and 20
ppm: Fe-20) and the control which does not contain added iron. The lowest concentration of
iron is based on the maximum tolerance limit for the discharge of industrial wastewater into
inland surface waters (3 ppm) which has been recommended by the Board of Investment (BOI)
of Sri Lanka. Fifteen male fish with an initial mean weight of 0.20±0.04 g were randomly
assigned in triplicated treatments and the experiment lasted for 45 days. Daily food
consumption and survival of the experimental fish were recorded and weight measurements of
fish were taken fortnightly. At the end of the experiment, growth performances and feed
utilization efficiencies were assessed by using percentage specific growth rate (%SGR),
percentage average daily gain (%ADG) and feed conversion ratio (FCR). Red blood cell count
(RBC), blood smears and histological variations of gill tissues of the experimental fish were also
examined at the end of the experiment. Mean body weight was not affected by the treatments.
There were no structural alterations observed in blood smears of fish in different treatments.
The lowest FCR (1.35±0.07) was observed in Fe-3 while the highest %ADG and %SGR both were
observed in the control (4.30±1.21 and 2.37±0.44). Significantly (p<0.05) the highest survival
rate (100%) was observed in control followed by Fe-3 (86.7±2.6%), Fe-5 (82.0±2.5%), Fe-10
(73.3±1.4%) and Fe-20 (10.0±0.7%). Among tested treatments, the highest RBC was reported in
the control and Fe-3 (1.83±0.30 ×106/mm3 and 1.92±0.49 ×106/mm3 respectively) followed by
Fe-5 (1.22±0.31 ×106/mm3), Fe-10 (0.99±0.21 ×106/mm3) and Fe-20 (0.61±0.13×106/mm3).
Histological sections of the gill tissues showed that secondary lamellae were arranged without
proper order and were visualized as broken or eroded, fused and misshaped filaments in the
high Fe levels. However, these alterations were not observed in the Fe-3. The results of this
study revealed that there is a significant effect of the chronic exposure of iron on the growth
performance, red blood cell counts and histological status of the gills of the guppy at the
concentrations greater than the BOI recommended level (3 ppm).
