Claire Corlett

Fish Food, Fish Tanks, and More
Algae Corner: Fish Kill Causes

Algae Corner: Fish Kill Causes

(light ambient music) – Welcome to the Algae Corner
with me Dr. West Bishop. What we’re gonna cover
today is why fish die. Now there’s a multitude of reasons why fish may die in your water resource. It’s never a good sight. It’s never a good happening. But it’s definitely something
that’s important to know, important to cover why fish
may die in your water body. Now the most common culprit of fish deaths is dissolved oxygen depletion. So fish need this dissolved oxygen in the water column to breathe, to live, and that dissolved oxygen may be depleted in many different ways. Now there’s natural
fluctuations in dissolved oxygen such as high plant or algal growth. Even if it’s good types
of plants or algae, they can cycle out. At
night time they respire, they use oxygen in the water column, and that can deplete oxygen
levels in your water body. Bacteria decomposition of organic matter is another reason why oxygen may be depleted in your water resource. Now this could be organic matter like leaves or grass clippings that just build up in the
bottom of your water resource that they’re using to
deplete those oxygen levels, or it may be from natural
cycling of dead algae, algal bloom that cycles
out, or a plant population that crashes either naturally or following an algaecide
or herbicide application. That depletion of dead organic matter from bacteria can be at play. Now, weather conditions
can also exaggerate this. If you have a lot of cloudy or rainy days, that can impede the natural
photosynthetic processes of algae and bacteria. Again, that can limit the
amount of natural oxygen that’s being produced
in the water resource, put more stress on the fish. There is often less dissolved oxygen that can be dissolved in the water body in these warmer, hotter temperatures, so if you have a lot of warm
days and hot temperature days, it can cause just innately less oxygen in the water resource,
stratification of the water, so those dissolved oxygen levels
get depleted even farther. So there’s many different
causes of fish kill, but often dissolved oxygen is the culprit of the most common types of
fish kills that we encounter, and there’s many reasons
that dissolved oxygen may be depleted. Now the next area we’re gonna talk about is other products that may run
off into your water resource. So there’s a lot of
terrestrially applied products that can end up in the water body that can pose risk to the
fish and cause a fish kill. These may be from a nearby parking lot, a sealant that was put on a parking lot. Stormwater runoff, there’s
a lot of constituents in stormwater that may
be toxic to aquatic life. Or even a terrestrially
applied insecticide, these can certainly cause risk to fish and other aquatic organisms if that gets too close to the water body or runs off into the water body. Another culprit of fish
kills are fish diseases, or parasites, or viruses. Now, often the fish have
diagnostic symptoms or clues if they have one of these,
so keep a close eye on them. But there are many different fish diseases that can cause mortality. One common one is called
ich or ichthyophthirius. This is an ecto-parasite, also
known as white spot disease, very diagnostic looking. But again, this can cause mortality. There’s many other fungal
infections or internal parasites like flukes or tapeworms that
can cause fish mortality. Another area, another thing
to keep any eye out for, is toxic algae. Now this is on the rise, and there are many different algae that can directly produce toxins that negatively impact fish. The golden algae, the haptophytes, can produce a number of
toxins that impact the gills. Some of the cyanobacteria
can have acute toxicity with the toxins they produce. And indeed, some euglenophytes or euglena can produce these fish killing toxins. So keep an eye out for toxic algae as well as a culprit to
potential fish kills. Now there’s many other areas, again, multitude of reasons, why fish can die, stress due to spawning, or old age, or just being overpopulated,
or overfed in a water resource. And there’s much information
that needs to be collected if you are encountering or
dealing with a fish kill. Take good pictures. Take detailed notes of all the occurrences that have led up to the event. You can sample your fish,
too, and freeze them and get them analyzed by a professional to see if there’s any diagnostic symptoms that they can pick out. Take a water sample. Have the water analyzed. The water chemistry, the
dissolved oxygen levels, all these can be very
useful in determining the cause of your fish kill. And we do have another
episode you should watch. So please see that episode
for more information. And well document the reasons you may be having a
fish kill in your site. And as always, if you
need help or assistance, we’re here to help. Please visit
for more information. (light ambient music)

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