RYAN, W.L.*; SCATCHARD, K.; BRADY, B.: Preliminary Findings from a Study of Gas Bubble Disease in Embryos and Fry of the Japanese Medaka (Oryzias latipes)

Gas bubble trauma is known to cause substantial morbidity and mortality of fish residing in gas supersaturated water. The trauma results from gas bubbles in the vascular system and other locations, causing a variety of physiological problems. Much interest in this topic is related to the controlled spilling of water from dams and the resulting gas supersaturation. Previous studies have examined the susceptibility of juvenile and adult fishes, but little work has been done to determine the response of developing stages to gas supersaturated conditions. This study focused on the exposure of embryos and newly hatched fry of the Japanese Medaka, Oryzias latipes, to very low gas supersaturations (ranging from 102 to 110% saturation). The gas supersaturation was established using a bubble column and was maintained for days at a time. Water was pumped from the aquarium and forced down an inner PVC pipe, exiting near the bottom of the column into an outer pipe, then ascended between the two pipes to the exit point and back to the tank. Air wands within the pipes generated the gas supersaturation. Each individual embryo or fry was observed daily for the diagnostic features of gas bubble disease and any other developmental abnormalities. In addition, digital images of each organism were analyzed in order to quantify the size of any gas bubbles or abnormalities present. Preliminary results show only a small percentage (<5%) of the embryos and fry exposed to these conditions showed abnormalities, none of which were characteristic of gas bubble trauma. In addition, no internal gas bubbles were observed. Further study is needed to fully characterize the response of the embryos to these potentially lethal environmental conditions.