MFSc

The present work was undertaken to study the effect of carbon dioxide anaesthesia
and packing density on Labeo rohita fry in oxygen - packed transportation. Hatchery
produced rohu fry of25 mm and 750 mg average length and weight were used for the
study. Sodium bicarbonate at three different concentrations viz., 0.2g 11, O.4g 11 and 0.6g
11 mixed with glacial acetic acid (mlll) in the ratio 2:1 in freshwater as the packing me-
dium was tried for in situ production of carbon dioxide anaesthesia. The fry were packed
at five packing densities viz., 100, 200, 300, 400 and 500 fryll under uniform initial
oxygen pressure of 0.2 Kg/ern" The behavioral pattern of the fry, induction time, recov-
ery time, safe duration of 100% survival and the subsequent duration down to 70%
survival were studied. The surviors were transferred to aerated freshwater without the
chemicals and were observed for 96 hours for subsequent survival.
Light sedation of the fry characterized by slow movement without losing equilib-
rium and with response to external stimuli was observed in the first dose of carbon
dioxide anaesthesia with an induction time of 10- 15 minutes. The recovery time was
not clear in the lower packing densities of 100,200 and 300 fryll, while it was 3 - 4
minutes at the higher packing densities of 400 and 500 fryll. The safe duration was
maximwn under this dose i.e., 39.0 h, 17.0 h, 10.0 h, 6.0 hand 3.0 hat 100,200,300,
400 and 500 fryll respectively. This was significantly different from the other two treat-
ments as well as control. By using this dose the safe duration could be enhanced 1.5 to
6 fold compared to the control depending on the packing densitity. Similar trend was
noticed at 90, 80 and 70% survival. The second and third doses resulted in deep sedation
characterized by slow movement without losing equilibriwn and with no response to


external stimuli. In the former dose the safe duration was more than that of the control
only at the higher packing densities of 400 and 500 fry/L In the latter case it was shorter
than that of the control and hence not at all practicable at any of the packing densities
tried. The recovered fry survived for the observed period of 96 hours. Linear relation
could be established between the packing densities and duration of transport for the first
and second dose as well as the control.
The water quality parameters of the oxygen - packed jars viz., dissolved oxygen,
free carbon dioxide, ammonia- N, total alkalinity and pH were analyzed initially, before
packing the fry, and finally at 70% survival of the fry. The final water quality in the jars
treated with the first dose was the least stressful for the fry, compared to the other doses
and control.