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Fish kill

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AlanMc

Well-Known Member
Sep 3, 2010
44
6
98
I was wondering if anyone has ever had a fish kill happen in their area, here in Grenada we recently had a fish kill happen where you would find many of our reef fish (snappers, parrot fish, etc. even eels) would be seen floating on the top of the water either dead or dying.

While diving all the fish seem fine, I never noticed any sick or dying fish and this is only happening to the fish that live in the reef.

All the floating fish and eels bellys were distended, many claim that it might have been because of low oxygen along with the warming of the sea may have caused the fish to die.

Has anyone else seen such fish kills or know of a reason why the reefs fish would be so affected?

Thanks

Alan
 
That sounds horrible, I hope it can be sorted.
The only thing I've seen that is similar is dynamiting in Indonesia.
Dead and dying fish on the bottom, some on the surface, only 1% of the dead fish are recovered, the rest don't float up to the surface straight away , not to mention the damage to the reef.
Me and the wife were in the water at the time, the explosions rattle your diaphragm and hurt your ears.
I hope nothing like that is going on where you are?
 
Some dumb arse playing with explosives seems likely.

What else then? A swell pouring in an invasion of alien toxic algae? It's happened before in many places, but non every day around. An epidemic disease? I've seen them, but they tend to hit one single species of fish, not all the species living on a reef.

Didn't you hear any explosion?
 
Thanks for the responses guys, no we do not allow fishing by explosive, actually you cannot even purchase explosives here.

This I believe is the second time this has happened in a few years but nobody seems to know for sure what is causing it. Some feel it may be an toxic alge bloom but we just don't know.

It really was not a nice thing to see.
 
I have studied this process and published some papers. The more frequent cause is the sudden blow out from the bottom sediment of H2S that is produced by bacterial sulphate reduction. This is a sort of anaerobic respiration and occurrs when the temperature of the water is high, the wind is very low and there is organic matter to be digested in the bottom. Low oxygen never cause fish kill because fish are able to swim where it is more abundant. Low wind cause low oxygen flux entering in the water column and bacteria use SO4 (sulphate) producing H2S that is toxic like cyanide.
The fact that most of fish killed are eels and bottom fish seems to confirm this hypotesis.
 
Agree with previous hypothosis and also consider the algal bloom we get here in the Gulf of Mexico called red tide. Last year killed tens of thousands of fish along Texas alone.

H2S croaked off all my pond fish once.
 
Hey Alan!
am from P.R., I remember growing up there and seen fish kills due to red tides.

Plus with all the storms in the Caribean, the extra rain and downpours in the islands usually flush a lot of fresh water & dirt into the oceans. Just a thought!
 
Hey Alan!
am from P.R., I remember growing up there and seen fish kills due to red tides.

Plus with all the storms in the Caribean, the extra rain and downpours in the islands usually flush a lot of fresh water & dirt into the oceans. Just a thought!


There was never any red tide down here atleast not that I could tell.

Gizzo your studies on the cause may be what has happened here, I do know people have seen coral bleaching starting on some of the reefs.

The kill seems to have passed as there are no more reports of dying fish anywhere on the island.
 
Unfortunately if the cause of the kill are not removed, it can happen yearly when the warm climatic conditions do not help the waters in exchanging oxygen with the atmosphere.
 
Unfortunately if the cause of the kill are not removed, it can happen yearly when the warm climatic conditions do not help the waters in exchanging oxygen with the atmosphere.

God I hope not, I do not think anyone found the root cause of the problem so if what you say is true then it could happen again.

I will keep my eyes open to see if this happens again.
 
Alan the cause is too much food for bacterial metabolism during warm summer. What arrived in the sediments these years ? A suggestion: collect a short (20 cm) core of sediment in a small plexiglass tube and look at the colour. Is it black or grey? If you send me a picture of the core I can say something.
 
Alan the cause is too much food for bacterial metabolism during warm summer. What arrived in the sediments these years ? A suggestion: collect a short (20 cm) core of sediment in a small plexiglass tube and look at the colour. Is it black or grey? If you send me a picture of the core I can say something.

I will try to get a sample, but the waters have already started to cleared up (it was dirty and silty because we somtimes get affected by the orinoco river in guyana during heavy rains )

I did not consider that it may have been some run off from the Orinoco because Trinidad is closer to the river mouth than us and they had no fish being killed.

We did have a very long dry season this year which normally is from November till June, July and the waters did not seem hotter than normal but I could be wrong since i have no means to measure the water temp. on a regular basis.

I will let you know once i have gotten the sample.

Alan
 
OK, let me know. If you can send me a link of the site or a picture of a map.
 
Last edited:
Actually i just watched a rather large documentary. and the algae blooms do create a zero or low to the leathal tolerance oxygen environment or hypoxic. And it looks the reason the fish do not swim away is these can be massive therefore by the time the fish in the center reach the edge back to rich oxygen supply there dead.Read the wiki link gizzo you might find it intreresting.
 
Dear NZ, believe me algal bloom is only an indirect cause of fish kill. If you monitor continuously Oxygen during algal bloom you will register a daily oscillation between an over saturation (up to 200%) at 6 o'clock p.m. to a strong depletion (close to zero%) at 6 o'clock a.m.
If you waste in a water body inorganic phosphorous you have an algal bloom that will bring to oxygen depletion; if you waste sewage you have directly oxygen depletion. In both cases bacteria have to decompose more organic matter and when oxygen is low they use SO4 (sulphate) and produce H2S.
 
oh im sure your correct im just repeating the words of scholers and scientists im architect not a scientist i have no interest in it now really. watched a documentry got over back to free diving
 
On the West Coast of Florida there are frequent massive fish kills like the one you describe. Literally millions of dying or dead fish all over the place. They make the beach impassable and the smell of the toxic algae gas even makes it hard to breathe some yards inland. It is caused by a red algae and referred to as "red tide". The algae is thought to be stimulated by all of the fertilizer runoff from developments and golf courses during the rainy season. Its disgusting and sad, but I have not seen any real progress in dealing with it in Florida.
 
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