Fish Behaving Badly

Is aluminium antisocial too?

Recently I came across a new paper describing aluminium as a 'behavioural disruptor' in fish. As many of you will already know I began my aluminium odyssey studying aluminium toxicity in fish and owe much of my understanding of human exposure to aluminium to this early work.

In my book I wrote the following about how juvenile salmon responded to an acute exposure to aluminium.

Some assaults on the senses imprint for life. One that remains with me is a smell that heralded salmon parr dead and dying from intoxication by aluminium. A parr is a juvenile salmon before it begins its journey from freshwater to the sea. I first encountered this fetid, though curiously sweet, aroma during undergraduate research into how aluminium interfered with the homing instinct of salmon. Well, death by aluminium proved to be the ultimate interference. Dead fish don’t migrate and don’t come home. Actually, as a brief aside, chronic intoxication by aluminium does interfere with homing instincts in salmon and this may be one very good explanation of the reduced numbers of returning salmon in rivers and streams impacted by acid rain. I wrote about this in my first scientific publication, a chapter in a book on how acid rain was affecting salmon farming.

This early research into aluminium toxicity in fish troubles me more now, nearly forty years later, than at the time. Observations of their death signatures, then recorded as disassociated data, feel strangely prescient when recalled today. Specifically so in the light of what we now know about aluminium’s role in neurodevelopmental and neurodegenerative disease. Aluminium, at a concentration allowed in potable water under European Union law, kills a salmon parr within forty-eight hours of first exposure. Only after eighteen hours do the fish show any obvious signs of distress. Their movements, within the confines of an experimental tank, begin to appear spasmodic, even frantic, as if searching for sanctuary from the poison. We learned only much later that fish actively avoid aluminium at concentrations less than one twentieth of the aforementioned acutely toxic amount. Quiet consolidation follows the escape response. Fish move towards the bottom and sides of the tank attempting to find solace away from wide-open spaces. They maintain this orientation, head pointed towards a corner of the tank, for as long as they have control over their actions. Before dying, their bodies stricken with involuntary muscle movements, they gasp at the surface of the tank, preferring air to their habitual water. The smell? Well this is evident within hours of death and may emanate from the copious quantities of mucus produced during the final thralls of life. Whatever its precise origin it is a harbinger of death and one which now haunts my every day.

Acute toxicity inevitably leading to death clearly invokes behavioural changes though whether these bear the signature of aluminium or simply dying is difficult to discern.

Perhaps more fascinating and even more relevant to the human condition are behavioural changes in fish brought about by distinctly chronic exposure.

Back in the ‘olden times’ before the invention of digital photography never mind video we studied fish behaviour using a simple camera and film that had to be sent away to be developed.

I also commissioned a local engineering company to build a bespoke exposure tank as you can see in the image below.

The image shows rainbow trout fry swimming in a Perspex cylindrical tank fed with water from the left and exiting from the right. You will note that the fish are more or less evenly distributed along the length of the tank.

Now, watch what happens when the incoming water from the left includes aluminium.

After just 2 minutes the distribution of the fish changes with more fish being present towards the outlet of the tank.

After 4 minutes more fish move towards the outlet.

Finally, 6 minutes after the introduction of aluminium at the inlet the majority of fish are found clustered at the outlet.

The rainbow trout given the opportunity actively avoid the aluminium-containing water at the inlet. Of course, within a relatively short time period all of the water in the tank is replaced with aluminium-containing water and the fish can no longer avoid it. You can read the details of this research in the published paper.

The most surprising even alarming aspect of this research was not that fish avoided water that contained aluminium, after all aluminium is toxic, but that fish avoided water that contained only 27ppb (27 microgram/L) total aluminium.

Today following the advent of The Aluminium Age there are few natural waters, by

which I mean rivers, lakes and streams, in northern Europe or North America (or indeed anywhere) where the concentration of aluminium is less than 27ppb. Avoidance is almost futile and the consequences for populations of anadromous fish such as salmon is there for all to see. Dwindling populations of wild salmon in rivers throughout the world.

Perhaps, like me, you are thinking that if salmon actively avoid aluminium concentrations as low as 27ppb then so should I. Unfortunately just like salmon it is almost inevitable that we are exposed to this level of aluminium on a daily basis. The activities of Man have ensured that living in The Aluminium Age means regular exposure to aluminium. Of course, we have the antidote and you have the ground breaking science described in my last post to help you to avoid the accumulation of aluminium in your body and particularly your brain.

A silicon-rich water a day will help to keep the doctor away.

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