What do gills do

If this is compounded by respiratory epithelial thickening encountered during disease, the outcome is unlikely to be positive—all of this, and there appears to be some, albeit non-validated, evidence that oxygen uptake across the gills may be limited in a warming world, possibly lowering fish growth and even threatening food security.

Our lack of understanding of the multifactorial nature of gill disease and the role of gill health within the context of overall fish health means we may be missing the true influence of gill disease on health and production. This is compounded with no clear way of assessing fish health based on gill health other than overt clinical disease with altered function and production in latter stages of presentation.

Mortalities arising from AGD may also be related to cardiac function rather than just the primary gill lesion, and cardiac health is potentially more important than gill health under global warming scenarios Powell et al. Despite being able to accurately describe gross and microscopic changes in the gills, interpreting those changes and any agent associated with those lesions requires the involvement of multiple disciplines. In addition to secondary infections by bacteria like T.

The role of Candidatus B. Merely identifying an organism does not necessarily answer any questions. Examination of the gill at the microscopic level is useful to reveal changes, such as chloride cell dynamics, and perhaps overall, histopathology is the most useful tool, particularly in the initial stages of assessing gill health Mitchell et al.

Nonetheless, in order to properly interpret results from histopathological evaluations, the literature shows that a healthy condition is not characterized by the complete absence of any histologically apparent traits, and an apparently healthy gill may display moderate alterations, such as minor structural disorders or mild inflammatory reactions Bernet et al. Fish gill function is already subject to excellent reviews Heisler, ; Evans, ; Brauner and Randall, ; Claiborne et al.

It is understood that eutrophication can have many effects in the anticipated future, but high environmental loading with nitrogenous compounds, such as ammonia and ammonium, will also affect osmoregulation, which would be expected to be exacerbated by gill tissue lesions. Investigation is still hampered by the lack of standardized respirometry methods, and the situation is further complicated by the fact that many fish gill functions are intertwined, a fact demonstrated by osmoregulation and acid—base regulation via the gills involving the same ion transporters but often working in opposite directions when environmental stress is applied.

Several species are known to use extensive remodeling of cell populations at the gill epithelium to regulate gill function in response to environmental change, and modest changes in gill morphology are commonly observed among a wide variety of species. This raises the question of whether gill remodeling will play a role in resilience and acclimation of fish to future environmental conditions with a limited number of studies finding gill remodeling in response to rising temperatures and the ocean acidification predicted to occur by the end of the century.

Unfortunately, potential benefits to the acclimation or resilience of gill functions remain unclear, and it will be important to consider the potential damaging effects of elevated temperatures and concurrent increases in the incidence of disease on gill morphology that may negate any beneficial effects of gill remodeling, leaving fish vulnerable.

It is clear that, in tropical zones, many aquacultured finfish species are farmed close to their thermal limit, leaving little room for a rising trend in oceanic temperatures. Fishes in these zones also have little room for gill remodeling that is likely to occur in parallel with increased levels of gill damage. Given the effect of temperature on host and pathogen metabolism, it is noted that progression of disease in the lower latitudes is more rapid and results in higher cumulative mortality Leung and Bates, with tropical producers suffering relatively more losses in aquaculture during disease outbreaks and having less time to initiate control and preventative measures compared to other regions.

That is not to say that finfish aquaculture in other areas would not suffer the consequences as well.

Atlantic salmon farming in Tasmania already occurs near the thermal limit for that species, and with sea temperatures expected to rise in the North Atlantic summers Bromley et al. Consequently, anticipated changes are thought of as a serious threat to sea bream Sparus aurata populations. Alternative locations and open-ocean farming have already been discussed, but future mitigation may also have to include breeding for increased tolerance to thermal stress and an understanding of how other climate variables might affect production, including the effect on agriculture, land use, and extreme weather events among others.

Fish health experts in conjunction with producers and laboratory-based scientists must work closely anyway but, in the future, will have to combine their efforts even more so with those of other disciplines, including but not limited to meteorology, oceanography, and environmental and social sciences. Indeed, all forms of intensive farming, terrestrial or aquatic, can negatively impact the environment, threatening sustainability.

This supports an even stronger argument for a holistic One Health approach to aquaculture but is considered beyond the remit of this review. The incidence of some infectious and non-infectious diseases will increase with climate change, and mitigation strategies must take into account global distribution of disease and vulnerability in aquaculture and develop options to minimize impacts on food production Bell et al.

Understanding the multifactorial nature of gill health and how it is impacted by anticipated climate change is central to this, and elevates the importance and relevance of gill health in food security and human well-being and not just in fish health. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Adams, M.

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Things are different for fish. Fishes also need oxygen, but rather than getting it from air, they have to get it from water. But there is less oxygen available in water than air. And to make matters worse for the poor fishes, water is thicker than air, so it takes much more work to move it around.

Rather than breathing in and out through the mouth, fish use a one-way system, passing water in one direction over their gills. Water goes in the mouth, across the gills and out through the opercula the bony covering protecting their gills. But gills and lungs are more similar than you might think. Both have really big surface areas which increases the amount of water or air that touches the gill or lung tissue, and so increases the amount of oxygen available.

This means the capillaries come into close contact with the air or water outside, letting oxygen pass across the thin walls and into the blood. At the same time, carbon dioxide, which is a waste product from our bodies, passes out. Hello, curious kids! Ask an adult to send your question to curiouskids theconversation. Read more: Curious Kids: when fish get thirsty do they drink sea water?