A meta‐analysis of gas bubble trauma in fish

Abstract

There is currently a worldwide proliferation of dams, with 59 000 hydroelectric dams over 15 m high registered with the International Commission On Large Dams (2018). Furthermore, there are an additional 3,700 hydroelectric dams over 1 megawatt (MW) planned or under construction as of 2015 (Zarfl, Lumsdon, Berlekamp, Tydecks, & Tockner, 2015). Once these dams are constructed, the number of large, free-flowing rivers worldwide will be further reduced by 21% (Zarfl et al., 2015). These numbers do not account for the proliferation of small hydroelectric dams; Couto and Olden (2018) estimate that there exist over 82,000 small hydropower dams worldwide (≤10 MW or based on each country's definition of small hydropower dams). Currently, only 37% of rivers longer than 1,000 kilometres are free-flowing over their entire length (Grill et al., 2019). Most new dams are being built in countries with developing and emerging economies (Zarfl et al., 2015), where important benefits include electricity generation, control of water supply, low flow

Fish and hyperoxia—From cardiorespiratory and biochemical adjustments to aquaculture and ecophysiology implications

“…Thus, if moderate levels of O 2 supplementation are used in fish rearing systems, for example to avoid hypoxia at increased stocking densities, care should be taken to avoid hyperbaric total gas pressures and unintended harmful impacts. Interestingly, a recent meta‐analysis of gas bubble disease in fish found that a higher O 2 to nitrogen ratio under conditions of increased total gas pressure actually improves resilience to gas bubble trauma (Pleizier et al., 2020). This is because O 2 , as opposed to nitrogen, is consumed by aerobic metabolism, which leads to a lower total gas pressure in the tissues than would otherwise be experienced at a particular level of increased total gas pressure (Pleizier et al., 2020).…”

Conservation behaviour in action: using fish behaviour to understand and mitigate the impacts of hydropower development

“…This occurs when atmospheric gases mix with the water passing through the gates, air bubbles become entrained, and the bubbles dissolve into the water in the plunge pool at the base of the spillway. Fish tissues and blood can become supersaturated with TDGs, they can accumulate and come out of solution (i.e., nucleate) under conditions of sudden changes in temperature and pressure, which can result in the development of gas bubble trauma (GBT) (Bouck 1980, Weitkamp and Katz 1980, Pleizier et al 2020a. As a result of GBT, bubbles can form in the fins, skin, or behind the eyes, whereas more severe injuries such as bubbles forming in the blood or gills can cause mortality.…”

“…Injury and mortality resulting from GBT depends on the duration and the level of TDG exposure. In Rainbow Trout (Oncorhynchus mykiss), mortality rarely occurs from exposure to < 110% TDG, takes roughly 10 days to occur at 110%, and can be as rapid as 2 h at 140% (Pleizier et al 2020a).…”

“…This means that when water passes over the spillway of a hydropower facility and plunges into the spill basin below, the atmospheric gases can dissolve into the water at depth and supersaturate the water to levels exceeding 100% saturation. Exposure to supersaturated TDG levels can be hazardous to fish occupying habitats downstream because it is known to cause gas bubble trauma (GBT) (Weitkamp and Katz 1980;Pleizier et al 2020a).…”

“…Exposure to TDG supersaturation >125% is known to produce GBT related fish mortality, though sensitivity varies among species and developmental stage (Weitkamp and Katz 1980;Wang et al 2015;Cao et al 2019;Ji et al 2019;Deng et al 2020). Exposure at low to moderate TDG levels (i.e., 105-120% supersaturation) can have sub-lethal effects (Pleizier et al 2020a;2020b), with fitness related implications (i.e., survival and reproduction) for fishes residing below large hydro dams (McGrath et al 2006). Since TDG supersaturation is a function of pressure (depth), hydrostatic compensation is possible such that a 1 m increase in depth roughly compensates for 10% TDG supersaturation (Bouck 1980;Pleizier et al 2020a;2020b).…”