The Conservation of Fish

The fish faunas of the world have been monitored for many years now, and while there is much we do not know, especially about the deep and open oceans one thing we do know is that the fish populations of all our water are undergoing a period of rapid change.

In the seas and oceans a number of fisheries have collapsed or are close to doing. This is because because over-fishing has so depleted the populations that it is now not possible to catch an economically viable number of this species. In many fresh water habitats introduced species are driving native species to extinction. Meanwhile, in all aquatic systems pollution and habitat destruction are reaping a dire crop, with decreasing fish populations and reduced diversity being commonly reported from a wide variety of localities.


A defaunated terrestrial habitat, an absence of bird life in particular or a degraded area of forest is easy to recognise, the declining bird populations of our countryside and the brutal pattern of stumps left after an episode of clear-felling are easy to photograph and to recognise as an insult to the world. However a degraded aquatic system is not so readily seen. Hidden beneath the vibrant curtain of the water's upper surface a degraded sea floor, dying coral reef or depauperate fish biodiversity often goes unnoticed by the general public.

However it is now known that the aquatic environments of this planet now contain some of the most damaged, degraded and destitute habitats in the world. Because they are smaller, and generally surrounded by human populations, it is the fresh water habitats of the world that are suffering the most. It is these same habitats that have for eons contained small, but thriving populations of endemic species with limited distributions. In other words those species least capable of finding an alternative habitat if theirs becomes unusable. Human beings confiscate much of the water from fresh water habitats, pollute what is left, interfere with the natural pattern of flow and introduce exotic species that damage or destroy parts of the endemic diversity and disrupt the precariously remaining balance of interactivity that is essential to the health of the system.

For centuries humanity has been deliberately destroying the wetlands, marshes, swamps and bogs that are essential to controlling the flow of water through, and the overall health of, many riverine systems; channelling rivers between raised banks to control and or prevent their flooding, damning them to retain their water and thus interfering with flow of water and the passage of nutrients through the system and on into the coastal marine environments where so many fish breed. Estuaries, marine marshes, tidal mud flats and mangrove forests have all been wantonly destroyed, and still are being destroyed, yet science has known for decades that all these peripheral areas are essential to the health and function of both our aquatic environments and the maintenance of our fish stocks.

In our human lungs it is the finest edges of the network of alveoli that take up the precious O2 we need every moment of our lives. In our bodies it is the smallest, most insignificant of our capillaries that deliver this O2 to our cells and thus allow us the wonder of life. If we were to remove all the smallest of the alveoli, or the finest web of capillaries we would soon become incapacitated, yet this is very thing that we are doing to the life blood of the planet. Every marsh we drain, every river we constrain, every creek we turn into a cement drainage ditch, every intertidal mudflat we build over or mangrove forest we dig out is like the removal of more and more of our lungs' essential aveoli. It cannot continue if we wish to remain healthy ourselves.

So yes, fish conservation is necessary, and fish conservation means habitat conservation, particularly aquatic and wetland habitats. It is in fact very necessary, but it is not easy, especially in marine habitats and with widely dispersed species. However before conservation can begin to work we need to change our attitude to aquatic environments, to start seeing them as the precious and well-designed resources that they are, so that we will not pollute, usurp or corrupt with exotic species their vital work.

Conservation of fish follows a number of interrelated courses. Firstly comes habitat protection, as part of a growing world-wide realisation that pollution is killing us as it kills the world many aquatic habitats have greatly improved over the last quarter on the 20th century. For particular efforts look to the return of salmon etc after the cleaning up of the Thames and other rivers in England and the recovery of the striped bass population of Chesapeake Bay USA. Some fresh water habitats have been improved as well, but there is still much more that needs to be done.

In particular governments are still failing to take environmental management seriously. As an example look at the case of Lake Koronia in Greece. A small to medium sized lake that has suffered both water reduction and pollution from shore based industries to such an extent that the wildlife that used to visit it have all left and the water is not fit for human consumption. European Union money was allocated for cleaning up Lake Koronia, but the massive ignorance and incompetence of the Greek government meant that the money was never claimed and the lake continues to shrink and and become more toxic.

Secondly control of fishing, times of fishing, size of fish and total number caught need to be regulated on a basis of the need to maintain and protect fish populations and not merely to satisfy the economic concerns of multinational companies. Furthermore international pressure needs to be brought on countries like Japan who still support fisheries for endangered species such as Bluefin Tuna (Thunnus thynnus). Commerce is a blind giant that must be made to accept its place as a servant of humanity if we are ever to succeed in living sustainably as a species, all too often these days commerce is erroneously elevated to the status of a god with disastrous consequences.

Also we need to invest in innovative ideas. While fishery management authorities have a long history of imposing minimum size criteria on legal catches, no-one has ever imposed a maximum size. The idea being that the largest and most successful representatives of a species should not be killed, but instead allowed to live on and produce as many offspring as possible, thus passing on their strong genetic pattern. If this had been done 50 years ago, with cod for instance, it may well have averted the forced evolution to smaller and smaller breeding size that modern overfishing has forced onto this species in the atlantic seas and ocean.

In some areas good work is being done, but one only has look at areas like Georges Bank, the Aral and Caspian Seas or any of the worlds 50 largest rivers to see what a bad job humanity is doing of living with and sustainably using, rather than just destroying, its amazing waters.

Extinct Species

One of the greatest ecological disasters of the world is the extinction of around 200 species of Cichlids from Lake Victoria in East Africa since the 1950s. The main cause has been the introduction of Nile Perch to the lake. However generally speaking the actual extinction of a species of fish is hard to prove. It is not enough to simply observe that the species has not been caught recently. To prove extinction it is necessary that a comprehensive survey be carried out, and in most cases this has not been done. However when a species of fish has not been seen for more than a decade it is a fair assumption that even if it is not yet extinct it must be close.

In researching this page I have found it hard to find two data source with a reasonable degree of congruity, so please be careful when quoting this or any data on fish extinctions. On the 6th of January 2008 the IUCN online database listed 80 species of fish and no sharks currently considered to be extinct, listed 96, but 7 of these listing were family names not species names leaving 89 and Wikipedia listed 28 but seem to confuse recently extinct with prehistoric in at least one case. Although the IUCN has reliable name I was impressed by the amount of information in downloadable Creo Extinct Fish database, while it is a bit comprehensive for secondary schools it seems scientifically rigorous. CREO stands for Committee on Recently Extinct Organisms, their database is available from their website at

The 2007 Creo Database information is interesting, it lists 177 species claimed to be extinct since the 1500s, but mostly in the last 100 years. Of these it disqualifies 13 claims on the basis that the species is now known to still be extant, and effectively disqualifies another two on the basis that they are incorrectly named. Of the rest it upholds 34 of the claims to extinction and leaves 128 unresolved, mostly because they say an adequate survey has not been carried out leaving us with insufficient data to resolve the species true position.


Here is a summary of the IUCN information available as of January 2008.
Ex = Extinct, Cr = Critically Endangered, EN = Endangered

Numbers of Extinct, Critically Endangered and Endangered species of fish, by Order. From IUCN 2007
Class + Order Class + Order Class + Order
Acanthoperygii Ex Cr En Acanthoperygii Ex Cr En Chondrichthyes Ex Cr En
Acipenseriformes 0 6 11 Mugiliformes 0 0 1 Carcharhiniformes 0 6 5
Atheriniformes 0 9 7 Osteoglossiformes 0 0 2 Rajiformes 0 11 20
Beloniformes 0 2 3 Perciformes 40 90 72 Squaliformes 0 1 0
Characiformes 0 2 2 Percopsiformes 0 1 0 Squatiniformes 0 3 4
Clupeiformes 0 1 2 Pleuronectiformes 0 0 1 Torpidiniformes 0 1 0
Cypriniformes 20 66 82 Salmoniformes 6 10 7 Subtotal Sharks and Rays 0 22 29
Cyprinodontiformes 12 25 19 Sorpaeniformes 1 2 2 Ex Cr En
Gadiformes 0 1 0 Siluriformes 1 11 12 Coelacanthiformes 1
Gasterosteiformes 0 2 1 Synbranchiformes 0 0 1
Gonorhychiformes 0 1 0 Subtotal Bony Fish 112 369 381
Lophiiformes 0 1 0
Ex Cr En
Total for All Fish 80 253 254

In total more than 80 species of fish have already gone extinct in modern times, this is far more than the number of birds, mammals, reptiles or amphibians, and yet far less is being done about their conservation. Scientists estimate that a minimum of 20% of all fresh water fish (about 2,100 species) will need special protection to stop them becoming extinct in the next 25 to 50 years.

Introduced Species

In two places in the world humanity has created a permanent link between two disparate marine environments. The first was the linking of the Eastern Mediterranean and the Red Sea via the Suez Canal, and the second was the construction of the Panama Canal. In both these cases two quite different populations of fish were suddenly put in contact with each other. The Suez "experiment" is older, and different because the water of the canal is either salty or brackish. In the case of the Panama Canal there is a central zone of fresh water that has acted as a effective barrier to fish migration.

The Suez situation is interesting to ecologists because it asks us interesting questions. Forty five species of fish from the Red Sea have successfully migrated along the canal and established themselves in the Eastern Mediterranean, thus gaining new habitat for them selves. Only three Mediterranean species have successfully made the opposite migration. Some reasons why may include the turbidity of the water within the canal, and the fact that the general flow of the water is from the Red Sea to the Mediterranean for most of the year.

Of course mankind has been deliberately, and accidentally, introducing fish from one habitat into another for thousands of years and many of these introduction have had important effects on local populations. In the last fifty years the number and variety of introductions has greatly increased. This is particularly true of countries such as Hawaii and the Philippines.

In terms of fresh water habitats earlier introduction were made deliberately to improve the fishing (Oncorhynchus mykiss), or to help control mosquito larva (Gambusia affinis) many more introductions however are either escapees from fish farming (Cyprinus carpio) or more recently rejects from the pet trade. Carassius auratus, the wild form of the common goldfish being the best example. In Hawaii and the philippines many introduced species are escaped, or released aquarium fish.

Table 2. Showing the total number of introduced species current in various countries as of 2007 and the presence or absence of the four most commonly introduced species : Gambusia affinis, Carassius auratus, Cyprinus carpio and Oncorhynchus mykiss.
Cent = Centrachidae, Ci ch= Cichlidae, Cypr = Cyprinidae, Poec =Poeciliidae, Salm =Salmonidae.
Country Total Cent Cich Cypr Poec Salm G. affinis C. auratus C. carpio O. mykiss
Eng + Wales 2 0 1 0 0 1 No No No No
Germany 21 2 0 5 0 5 No Yes Yes Yes
Greece 30 1 0 7 2 1 Yes Yes Yes Yes
Ghana 3 0 1 1 1 0 Yes No Yes No
Kenya 17 1 6 3 4 2 Yes No Yes Yes
S. Africa 20 5 3 5 3 2 Yes Yes Yes Yes
Israel 50 0 2 6 3 2 Yes Yes Yes Yes
Afghanistan 10 0 0 7 1 7 Yes Yes Yes Yes
India 19 0 2 8 4 3 Yes Yes Yes Yes
Russia 26 2 6 6 3 1 Yes Yes No No
China 28 1 4 7 1 2 Yes No No Yes
Thailand 20 0 7 8 3 0 Yes Yes Yes No
Australia 31 0 5 6 8 5 Yes Yes Yes Yes
Philippines 40 3 7 9 4 0 Yes Yes Yes No
Hawaii 69 4 18 1 9 1 Yes Yes Yes Yes
USA 49 0 19 9 1 0 No No Yes No
Costa Rica 11 0 4 4 2 0 No Yes Yes Yes
Brazil 15 1 5 4 0 1 No Yes Yes Yes
Guyana 5 0 1 3 0 1 Yes Yes Yes No

Recording the introduction of marine species is often more difficult, however it happens quite frequently. Ships sailing around the world take on water from one port to use as ballast and then pump it out in another thousands of miles away. Not only fish but a whole range of marine creatures have been able to colonize new habitats around the world with the help of mankind in this way. While legislation has been introduced in some countried to control this problem these rules are often poorly enforced and ship owners often seem to care very little for the environment on which they make their living, more still needs to be done and quickly.

Whether they are accidental or deliberate such introductions change the balance of forces within a habitat. While they can sometimes have beneficial in terms of increased food fisheries for humanity they can equally have a negative effect on fisheries as when an introduced and less edible, or commercially viable species out-competes a local species. Whatever the effect in terms of human fisheries they are normally disastrous for the local fauna. The most striking example of this is the extinction of 200 plus species of cichlids from Lake Victoria following the introduction of the Nile Perch (Lates sp.) in the 1950s.





The Fish Anatomy Menu
Anatomy Fins Blood Nerves Magnetism Swim-bladder
Skeleton Sight Scales Hearing Electricity Osmoregulation
Digestion Gills Smell Muscles Lateral Line Thermoregulation



Have You Seen The Other Earthlife Web Chapters
The Home Page of the Fish The Birds Home Page The Insects Home Page The Mammals Home Page The Prokaryotes Home Page The Lichens Home Page

Index Gif               



This page was designed and written by Mr Gordon Ramel



Advertising Inquiries

         Disclaimer, Copyright and Privacy