The secret life of fish

Fish talk to each other, they are intelligent, and learn behaviours much faster than you’d think – they are thinking, feeling creatures with individual personalities and complex needs.

In this article aquatics tutor, David Cooper, helps us delve into the secret life of fish.

So, besides the obvious, how different are fish from humans? If you investigate their inner workings, they are as sophisticated as us in what they need to live a happy and healthy life.

First, safety in numbers. “Many fish need to be kept in schools to ‘feel’ comfortable,” explains David.

In the wild, fish are surrounded by predators and must be acutely aware of their environment to keep themselves and their peers safe from harm. "Scientific research has shown that fish can actually sense a predator in the water from the pheromone trail that other animals leave, even if they cannot see it."

But, don’t be fooled in thinking that all fish are the same. “Some species of fish need to be kept alone in captivity. These are normally large territorial, predatory fish. Other fish kept with them are simply territorial threats or potential meals and aggression inevitably occurs,” says David.

Depending on what species of fish you own, they have different needs to live a happy and healthy life. Size does truly matter when it comes to the environment, we keep them in. Fish need to be kept in a filtered, spacious, enriched aquarium to offer them a good quality of life.

“Typical goldfish bowls are much too small. Filtered and good quality water is hard to maintain in a space that small and there is definitely lack of environmental enrichment,” says David.

“In the wild goldfish would be in complex environment, such as a pond or river with plants, other fish, rocks, logs, variable flows and a variety of foods. I have met people who have said to me ‘well I had a goldfish in a bowl for 10 years and it was fine’. My answer is that firstly they are the rare exception rather than the rule, and secondly that doesn’t make it okay. A small bowl or tank does not offer them the quality of life they need.”

We’ve all heard the saying ‘memory of a goldfish’ but fish are much more intelligent and have a better memory than they get credit for.

Fish can be taught to remember many things, including how to perform complex tasks. “A scientific study by Culum Brown in Australia focused on teaching a group of Rainbowfish a spatial learning task, \ requiring them to memorise an escape route. This involved a maze style set up in a tank, where certain parts of the maze had treats available for the fish.”

“After teaching them this task, the fish were then retested twelve months later, and they remembered the layout of the maze. These are fish that normally live 36 months so for 30% of their lives they retained this knowledge which is fascinating,” says David.

“Anyone who keeps a goldfish pond and feeds the fish at the same time each day knows they remember because they will all be congregating at the feed point every day and on time!”

Some species of fish can live up to 40 years of age and can recall human and fish faces, different tanks, spaces and colours. If you feel like your fish recognize you, you’re probably right! One research study in 2012 revealed that fish can outperform primates on memory tests and have been proven to be able to learn to use tools. Some fish also have large brains in relation to their body size because they receive information through electroreception. This is a special sense that gives them the ability to detect electrical currents omitted from other animals and organisms in the water.

A fish’s memory continues to fascinate, as David explains, “One of the biggest things that might surprise people about fish is their memory and ability to interact. I have a friend with a large South American Cichlid fish which is a predatory fish and very intelligent. The fish likes to watch Coronation Street and can see the TV from its tank and is indifferent to most programmes. When Coronation Street comes on the fish watches from the tank intently and if you change the channel it thrashes around as if annoyed.”

Fish are so different to humans on first appearance we may assume they cannot experience feelings or communicate. To an untrained eye, it may be easy to miss important interactions. Research has revealed that fish have many vocalisations they use to communicate with one another – but as they are made underwater all the human ear picks up on is silence and the odd ripple of the water. Fish not only vocalise, fish species use a variety of inventive ways to communicate; making sounds by vibrating their swim bladders or jiggling their gill covers, elaborate visual displays, and some species have even been found to use “flatulence communication”!

Fish are emotive creatures, in tune with other fish and their surroundings. “We often use the term “community fish”, which relates to fish that will live together reasonably harmoniously. There may be various species and from various parts of the world, but they share similar water quality and food requirements and are not overly aggressive nor grow too big,” explains David.

Scientific testing reveals the various emotions fish can feel. “The development of cortisol (stress hormone) tests that tracks cortisol levels released in the water fish are kept in indicate that fish certainly feel stress under many circumstances,” says David. Like humans, fish avoid painful or unpleasant situations and seek out pleasurable ones. Some aquarium fish have been observed showing play behavior, such as riding bubble streams and throwing objects around their tank!

When it comes to socialising with each other, research reveals that fish have a complex social hierarchy and don’t just stay in schools of large numbers for safety – they can remember their mate and like to stay close by because of the bond they have established. Experiments show that they can become emotionally attached to their partner and, if separated from them, display signs of depression.

“Many schools have social hierarchies with dominant and submissive fish. If the school size becomes too small this can be problematic as the fish at the bottom of the ladder get excessively harassed by the dominant fish. There are also a number of fish species that exhibit parental care - it’s fascinating,” says David.

Not only do fish constantly surprise us with their emotional interactions with each other, but they have been known to interact with people too. “I worked in a store where we had an Emperor Snapper, a large marine predator who was kept in the staff lunchroom in a large tank as it had outgrown the available display tank. It soon figured out that if it sprayed water at somebody sitting at the lunchroom table through a gap in the lid its chances of sharing your lunch was increased.”

“I like to tell these kinds of stories as they tend to break people's stereotypical attitudes towards fish.”

There is so much we are still learning about fish but most of all we are learning that they are far more complex than we had previously thought. As our knowledge of how fish experience the world expands it has implications for how we interact with them.