101 ways to kill fish
Patrick Haughton, Sparsholt College, takes a lighthearted look at mortalities, but the underlying message is serious
WHILE working on your fish farm, do you ever wonder why you do the job? Is it the pay? Is it the long holidays or, maybe, the glamorous environment? Occasionally I ask myself this question (usually at 2am when I am cleaning the screens during a thunderstorm!).
Why do I continue to look forward to the next batch of fish or the new season? On reflection, it is because I never get it right. To put it bluntly, every year I discover a new way to kill fish! If you are an animal welfare officer, let me assure you that my goal is to rear healthy, vibrant fish profitably. However, it is an inevitable consequence of farming fish that they will die due to mistakes, poor technology, bad husbandry and, sometimes, bad luck. The competition of the free market means that the commercial operator walks a tightrope. Since we farm to the limit of our resources, the borderline between success and failure is narrow and the transition is fast, painful and usually expensive.
As a child I remember bringing a bucket of blennies up to our holiday cottage to show my parents. After they had been suitably inspected and my fishing prowess complimented, they were left outside, to be returned the following morning. I was to experience my first fish kill…
But my first loss of fish on a large scale was in the winter of 1978. Massive snow-falls over the fry ponds collapsed the netting and blocked the screens. We worked through the night in appalling weather to minimise the losses. At least I had not been responsible, but burying skip-loads of fish made a lasting impression on me. Such depressing work! Cannibalism
The second big loss occurred when a wooden screen collapsed overnight and fingerling trout from a pond above found themselves sharing the pond below with some voracious second-year brown trout. I was first to arrive on the scene and, after skipping from one foot to the other and flapping my arms, I rushed off to find a seine net. While I was running around, the manager took stock of the situation, picked up a bucket of food and started feeding the pond. As if by magic the brownies stopped gorging themselves on the fingerlings and satiated their appetite on pellets. We were then able to solve the problem at our leisure. Not long after that, we installed metal instead of wooden screens. Since those early days, I have made all the standard mistakes: wrong dose calculations; overstocking; forgetting to put back the airstone, raise the standpipe or turn the flow on again. These have all resulted in small losses, near-misses and sometimes major disasters. One hundred thousand orfe fry, stocked into a recirculation unit before I had dechlorinated the water, is my worst calamity to date.
Drowning
In an effort to reduce the number of fish that die each year, I have here recorded some of the more unusual fish kills that I have experienced or been told about.
This unusual mortality happened to an entire tank of snakeheads. The tank had been fitted with a lid because the snakeheads, as ‘air breathers’, had a propensity to escape. However, after the lid had been fitted, the tank was then filled to the level of the lid leaving the fish with no opportunity to breathe air.
When we strip our tench, we do 20 or so fish at a time. They are