The vast majority of information describing the effects of DGS on fresh water and marine organisms is for Pacific salmon and trout species. There is only limited information on other fresh water and marine fish species. The situation is much the same for fresh water and marine invertebrates and there is essentially no information on fresh water and marine plants or algae. As a result, it is not certain that the guidelines derived herein would be protective of all fresh water and marine organisms under all environmental conditions. Based on these deficiencies, there is an immediate need for experimental data on fresh water and marine fish species other than Pacific salmon and trout. For example, in British Columbia, white sturgeon inhabit some of the rivers having the highest levels of DGS (Hildebrand 1991). There is no information on the effects of DGS on this species. In addition, experimental data is needed for fresh water and marine invertebrates as well as fresh water and marine plants and algae. Once these data are developed, they should be incorporated into the GBT threshold equations and guidelines where appropriate. This may require revising the equations to apply to specific species or environmental conditions.
DGS resulting from solar heating, perhaps combined with oxygen production from photosynthesis, has been identified as the cause of major fish kills in locations outside British Columbia. Fish kills of unknown source have occurred in lakes and marine environments in British Columbia under conditions which could have involved DGS caused by solar heating and photosynthesis. Since DGS has not been monitored in these situations, an educational program is needed to make fisheries officers and biologists aware of this effect. In addition, instrumentation should be provided along with the necessary expertise for measuring dissolved gas tensions at the time fish kills occur. This should include the availability of personnel with the expertise needed to identify the signs of GBT in fish. In addition, a research program should be initiated which identifies the environmental, physical, chemical, and biological parameters which control the development of DGS under conditions of solar heating and photosynthesis, and which also identifies the mechanisms which lead to fish mortality. If a contributing factor to high levels of DGS is the discharge of nutrients by industry, municipalities, and agriculture into water courses, provisions should be made to either limit these discharges and/or identify the conditions under which they would not threaten aquatic environments from DGS.
There needs to be additional research conducted to establish how DGS affects fish behaviour in terms of the use of the swim bladder. As pointed out earlier, small fish could be forced into deeper water environments to compensate for over-buoyancy caused by DGS. This may represent a greater threat to survival in terms of exposure to predators. On the other hand, the presence of DGS may allow a small fish to stay in deeper water without the need to return to the water surface to refill the swim bladder. This may lead to reduced exposure to predators which might be encountered in the trips to and from the surface. At this point, it is not clear what the net effect on survival may be as a result of these responses.
There needs to be research conducted which would establish the response of young fish to DGS under conditions of low water pO2. The intent of this research would be to establish if fish would remain at the water surface where dissolved oxygen content is higher or would they move to a lower water depth to compensate for over-buoyancy.
Finally, there is need for research on the effects of DGS on physoclist fishes. To date there is almost no information available for these species.