Fish Farm - Thousands Die - Why ?

[Speedo1968]

I have been involved in farming since 1961 though never with fish.

My work, freelance, took me to many countries including Thailand.

I spent many years with duck on projects large and small.

The following question relates to an event that happened some years ago and it still puzzles me today.

One very large, well established family farm had duck houses with bamboo slated floors, each containing 10,000 - 20,000 commercial ducks ) over large ponds.  

Some ponds had no houses over them.

During a three day visit it rained very hard on one night ( rainstorm ? ).    The following morning hundreds of thousands of fish were found to have died.

It was estimated that numbers totaled close to one million.   The farm owners had never seen anything like it.

 

Could anyone tell me what may have happened ?

 

As the event occurred overnight and the fish had been healthy I cannot guess what happened.  

Could it have been over or under oxygenation, sudden change in pH, nitrogen levelsetc. from ducks droppings that fall through the slats ( the duck houses were stocked with older birds and had not been cleaned ) ?

[canuckamuck]

O2 content in water drops when it rains. It could be that the levels were already low.

Duck poop would have been elevating the levels of nitrates which in itself could kill fish, or more likely caused an algae bloom which would have lowered the O2 in the water.

Generally speaking fish farmers try to eliminate waste in the water to increase fish health and appetite. The duck waste may have been feeding the fish, but it may have also created a tipping point for the water chemistry. The heavy rain was the final straw.

[RichCor]

Don't disregard the possibility of a nearby lightning strike.

 

Otherwise, would be interesting to know if any of the fish population survived, and what were the differing conditions for their pond environment. Though I Would assume that once you have a large enough fish kill that the availability of surface oxygen would fall and deprive the rest remaining in the pond.

 

[carlyai]

Çould also be combined with a quick change in water ph as well as the lack of oxygen.
I've heard it happen before because of algae bloom.

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[worgeordie]

Maybe a rapid rise in Ammonia from the Duck shit

been suddenly flushed into the water.that's my thoughts.

regards worgeordie

[Speedo1968]

On 2/23/2018 at 12:03 PM, carlyai said:

Could also be combined with a quick change in water ph as well as the lack of oxygen.
I've heard it happen before because of algae bloom.

Sent from my SM-J700F using Tapatalk
 

Many thanks 'carlyai' for your response.

There had apparently been no algae bloom, which was my first consideration too, have seen devastating losses with farmed ducks due to algae.

I have no idea about suitable pH levels for farmed fish.

I wonder if over oxygenation is possible due to rain ?

The owner of the fish farm had never in all his long years never seen anything like it before.

[Speedo1968]

On 2/25/2018 at 9:03 AM, worgeordie said:

Maybe a rapid rise in Ammonia from the Duck shit

been suddenly flushed into the water.that's my thoughts.

regards worgeordie

Many thanks 'worgeordie' for your thoughts.

The duck poo would not have been washed out of the houses due to the rain as the building were, despite their age, in good state of repair.    

The floor was of bamboo slats which did not / were not cleaned during the 7 - 8 weeks the ducks were there, only cleaned out at the end of the crop.

There had been no algae blooms before or after the rain, the ducks were found dead directly after the rainstorm on the one night.

Perhaps your right in that the rain fell hard enough to create turbulence in the water and dragged up the ammonia.

[Speedo1968]

On 2/22/2018 at 5:29 PM, canuckamuck said:

O2 content in water drops when it rains. It could be that the levels were already low.

Duck poop would have been elevating the levels of nitrates which in itself could kill fish, or more likely caused an algae bloom which would have lowered the O2 in the water.

Generally speaking fish farmers try to eliminate waste in the water to increase fish health and appetite. The duck waste may have been feeding the fish, but it may have also created a tipping point for the water chemistry. The heavy rain was the final straw.

Many thanks 'canuckamuck' for your interesting response.

There had been no algae blooms before or after the rain, the ducks were found dead directly after the rainstorm on the one night.

I thought that O2 levels would have increased in the ponds if it was bound into the large drops of rain.   I didn't realise that O2 drops when it rains.

The final line of your post probably sums it up - not enough oxygen.

The farmer, despite his many many years in the business had never seen anything like it before.

[Speedo1968]

On 2/22/2018 at 6:07 PM, RichCor said:

Don't disregard the possibility of a nearby lightning strike.

 

Otherwise, would be interesting to know if any of the fish population survived, and what were the differing conditions for their pond environment. Though I Would assume that once you have a large enough fish kill that the availability of surface oxygen would fall and deprive the rest remaining in the pond.

 

Many thanks 'RichCor' for your interesting possible cause - a lightening strike.

Most if not all fish were found dead in the early morning at first inspection by the farmer.

All ponds were affected and all fish died during the night of the storm.

If I remember the farmer, who had NEVER seen anything like it in all his years, commented that the fish were found floating on the surface.

Unfortunately I have no idea if any autopsies were carried out or, as to if he emptied the very large ponds before restocking.

The ducks at the farm were unaffected.

[RichCor]

That know-it-all mr google search seems to agree with the other posters, with the search results having a consensus of:

 

Fish Kill "tends to occur due to temperature or pH shock after a heavy rain event, rapid temperature changes in the shallows, or localized oxygen depletions, especially in areas of heavy aquatic vegetation. Heavy rains can cause large amounts of runoff that differs in pH and other chemical properties"

 

Google Search for: Fish Kill after heavy rains

 

Alternative Theory: Dihydrogen Monoxide Poisoning. They Drowned.