When buying fresh fish at the market, you may have noticed that they come in different shades and colours.

Fish occur in almost every colour imaginable, including red, blue, green, yellow, orange, brown, black and silver. Brightly coloured fish are mostly found in the oceans, while those with shiny silver, greyish, greenish or silvery bodies, often with pale or dark fins, are more common in inland waters such as lakes and rivers.

At the market, fish of the same species can sometimes have strikingly different colours. This has led some people to believe that their taste must also be different.

But experts say colour itself does not physically alter the taste of fish. Rather, it can influence perception, with the brain sometimes associating an unusual appearance with an unfamiliar or undesirable flavour.

If a fish looks different from what a person expects, the brain may interpret its taste as being off or unappealing. It is partly why some people insist that certain fish simply do not taste good.

According to marine experts, fish colouration is largely an adaptation to the environment in which they live. Their skin can change colour when they move from one environment to another.

Michael Omondi, the Aquaculture Business Development Programme (ABDP) Coordinator in Homa Bay, says skin colour is primarily an adaptation that helps fish evade predators.

Tilapia, for example, can become light and silvery when living in dark water. In clear water, however, it can become darker.

Mr Omondi says the different shades help fish evade predators both above and below the water.

“Fish use their colours to avoid birds by blending into their surroundings or confusing the predator. A bird looking down sees the dark back blend into the dark deep water. A fish or predator looking up from below sees the light belly blend into the bright sky,” he says.

Also Read: Lake vs pond fish: How to tell an ‘original’ tilapia from a ‘fake’ one

Women clean Tilapia fish captured from Lake Victoria.

Photo credit: File | Nation Media Group

The fisheries expert explains that this is why fish living in open waters of the lake, cages and ponds can have different colours despite belonging to the same species.

Fish kept in cages, for instance, tend to be darker, while those in open water are generally more silvery.

Mr Omondi says fish kept in crowded areas, where they have little opportunity to escape, tend to become darker as a camouflage mechanism against birds of prey.

When birds look down into the water, the darker fish are less likely to catch their attention because their skin reflects less light.

Fish kept in ponds can also develop a darker colour.

“Being dark does not mean total black. If we are having fish which are all silvery and then you find one which is very black like charcoal and with red eyes, that is a sign of malnutrition,” the fisheries expert says.

By contrast, fish that can move freely to different parts of the lake tend to develop lighter skin.

Fish can alter the pigmentation of their skin when moved from one environment to another as a means of survival.

They have specialised skin cells called chromatophores, which contain different coloured pigments. Their brains sense changes in the background and light levels, then send signals that cause these pigment cells to expand or contract.

This enables fish to change colour rapidly, helping them hide from predators or blend into their surroundings.

Rio Fish founder Angela Odero displays fried tilapia.

Photo credit: Pool

Moving to a new environment can also cause stress, fear or excitement, triggering rapid fading or darkening.

Mr Omondi says fish kept in cages can change from dark to silvery when moved into open water.

This, he says, helps settle the debate over whether the colour of fish affects its taste.

However, while colour itself does not determine taste, fish from different environments can acquire slightly different flavours, particularly when freshly boiled.

Mr Omondi says taste is also influenced by the food fish consume and the quality of the water in which they live.

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“Fish found in water which is alkaline in nature tends to taste differently from the ones found in fresh water. Alkaline means it has calcium carbonate; it would tend to have some natural salty taste,” the ABDP coordinator explains.

He says fish found in clear water tend to have less of the natural salty taste.

Fish living in silty or muddy water, meanwhile, can acquire a distinctive earthy flavour.

“All these tastes can only be noticed when you are cooking your fish fresh-boiled. That is when somebody would say fish was salty or sweet,” Mr Omondi says.

He adds: “Some particular kind of fish feed would also slightly bring in the issue of taste.”

This means fish from different parts of the lake can taste differently, with those from less polluted areas potentially differing from those found in more polluted sections.

Mr Omondi says water in the Winam Gulf, stretching from Rusinga to Siaya and all the way to Kisumu Dunga Beach, is more polluted than other parts of the lake.

In the Winam Gulf, the water is slightly turbid and brownish, while the area is also heavily infested with water hyacinth.

Mr Omondi says water quality changes as one moves away from the source.

“Water quality will affect the health of fish, the size of growth, the type of fish which will survive in the area and their colour. At a slightly lower level, it will affect the taste,” he says.

Deep fried fish — Deep fried tilapia.

Photo credit: File | Nation Media Group

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The fisheries scientist says Nile perch found in the Gulf tend to be silvery and slim, while those in waters towards Mfangano Island, where the lake is relatively clear, are usually slightly fatter and darker.

“The slim one does not have that strong Nile perch smell and fatty Nile perch oil. This affects value addition. If you want to smoke, the fatty one will smoke very nicely for you and will give you a good taste. The slim one will not,” he says.

He adds: “When frying, the slim one will fry very nicely but the fatty one will mix its fat with the oil being used. So that would mean if you want to spice, maybe the fatty one, you make fillet out of it and then you add your spices. For the slim one, you just have to fry it the way it is and you eat it.”

Meanwhile, as water becomes more polluted, oxygen levels fall and Nile perch may move to areas with better conditions.

Mr Omondi notes that low oxygen levels also affect omena (silver cyprinid).

“To some extent, tilapia tends to survive in low oxygen. But when it gets too low, the fish will either move or die,” the fisheries expert says.

The fish that can survive in severely oxygen-depleted waters include mumi (catfish) and kamongo (lungfish).

This helps explain why open waters with a greater supply of oxygen tend to have omena and , rather than catfish or lungfish.

Other sections of the lake are home to okoko and ochong’a (shrimp).

Fish are remarkably adaptable creatures, and some species can even reverse their sex as a survival mechanism.

Mr Omondi says that when an entire population is female, one fish can change sex and become male, helping prevent the population from being wiped out.

Those that undergo the change can then breed with the others, allowing the population to survive.

In commercial fish production, farmers can induce sex reversal while fish are still young by giving them hormonal feeds.

Mr Omondi says an increase in water temperature can also cause female fish in a group to develop into males.

“It is not the most effective way of converting them to males. The best system is the use of hormones. But if the treatment goes down, they reverse back. So the females, which were males, reverse back again to females,” the fisheries expert notes.

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