Dr M.I. Ahmed is a specialist in aquatic medicine with the Department of Veterinary Microbiology and Parasitology, Faculty of Veterinary Medicine, University of Maiduguri. He has done a lot of research on heavy metal content in fish in the Lake Chad. In this interview, he explains how global warming has forced some fishermen to use organophosphorus chemicals to catch fish and the implications of eating this fish by man.

Tell us about your research on heavy metal content in fish in the wetlands of Yobe.

Yes, I did some work in Yobe, and I realised that River Yobe is a good water body for fish production but, like most inland waters, it has heavy metal deposits in them and fish, as you know, is an important dietary protein. And again, there are other important aspects of fish like fish oil that contains Omega 3 fatty acids, which is a very important medicinal product. In this area, fish is not only a source of livestock protein, it also helps fishermen to earn a living.

How has climate change affected this important aspect of people's lives?

Climate change, as a result of global warming, has affected particularly countries in sub- Saharan Africa in the sense that it has affected their production as well as resulted in the prevalence of diseases in their environment. And again, the change in temperature has also indirectly affected their health because fish prefers a particular temperature range for it to be comfortable and for it to be productive.

With this low production and rapid population growth, don't you think man will be desperate in his search for survival?

Actually the feral fish that we depend on (that is, catching fish in the wild) is dwindling greatly both as a result of global warming and as a result of indiscriminate use of fishing gears. There are certain sizes of fish that should be caught but, unfortunately, because of the desperate position of the artisan fishermen around these water bodies, they use what we called taru, a fishing gear that is, honestly, criminal to use. It catches not only table size fish but even fingerlings; this takes away everything from the water, rendering it barren.

This translates to deficiency in protein in the population of the immediate community. People have to lean on other forms of protein from larger livestock which is not certainly easy to come by. The prices are going higher as a result of global warming too.

The implication of all these, when the artisan fisherman becomes desperate, [is that] he can go to the extent of poisoning the water where he cannot reach with his fishing gears. He may use some chemicals such as insecticide, called Gamalin, which is an organophosphorus compound. It is used to poison the fish so that the fish will float on the surface of the water. But mind you, this is at a cost because you are not only poisoning the fish but also man, at the top of the food chain, who is feeding on these fish and the water he drinks and even the crops he grows in the vicinity.

Man will be faced with the problem of bio-accumulation of these heavy metals in his body, particularly in the brain, the kidney and in the liver tissues. The implication of these toxic metals in humans is associated with central nervous system disturbances and cancerous diseases.

Are the activities of the dry season farmers who apply fertilizers to their farms by the shores of these water points causing the same problems?

Yes, farming in these wetlands results in the leaching of synthetic fertilizers into the water and can best be described as a fluid within a fluid; such an association what ever is found in this environment will go into the fish because it takes in a lot of this water involuntarily or voluntarily and it is absorbed within its gills, the gills area have some epithelium where exchange of gas takes place.

Even the crops that are grown from organic fertilizers in the developed world, they have a premium price than with synthetic fertilizers because of bio-accumulation. If one eats these plants grown with synthetic fertilizers it accumulates in your body over time and because it is not degradable it triggers one or two forms of diseases.

In specific terms, how do these chemicals affect their victims?

These chemicals end up in the tissues at different [levels of] concentration. They accumulate in different tissues of the fish and we don't look at fish as one and the same thing. We have the muscle, the kidney, the liver and others, so the concentration of these toxic chemicals varies with different tissues. If you look at the liver, it varies because it is the detoxification centre of the body of any living creature.

When these chemicals are taken in large quantities by fish, they become toxic; as a result, the oxygen-carrying capacity of the blood will be hampered. Again, the mere presence of GamalinR or DDT on the surface of the water also reduces the oxygen absorption of that water at that level. That is to say, when you have a large quantity of organophosphorus taken in by the fish it will be absorbed through the intestine, then the blood system, then the red blood cells that carry oxygen to the tissues will be impaired while tissue respiration will be affected and they will be damage to those tissues.