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E.I. Nnadi
Department of Biology, Alvan Ikoku Federal College of Education, Owerri
K.U. Nnadi
Department of Maritime Management Technology, Federal University of Technology, Owerri



The paper addresses the incontrovertible fact that fish and fish products have historically been a reliable supplier of protein, in particular, and food, in general for humans. Seventy to a hundred metric tons arc caught each year since the early seventies. Fish protein represents about twenty five percent of the total animal protein consumed by the world's population, second only to beef. This constitutes a significant contribution to the two thousand five hundred calories (more precisely kilocalories), the energy needs of the average person. In this capacity, fish arc amassed from both wild and domesticated sources. The paper notes regrettably, however that fish stocks are currently found to be on the decline. A major factor implicated in the causation of this adverse trend is the group of organisms and microorganisms known as fish parasites. The most notorious among these are the lampreys, some of the acanthocephalans, and the copepods. The alarm is raised in the paper that this combined scourge of fish farming, fish production and fish availability must be brought under control as part of the general food security strategy. The paper posits that the adoption of tested chemicals, selective in action, could be instrumental to the checking of the excesses of theravaging and rampaging parasitic infections.

Keywords: Fish; food; protein; parasites.


Currently the world population stands at about six billion people on earth. World-wide the majority of people live in less-developed countries. Because of their higher population growth rates, less-developed countries will make the greatest contribution to world population growth over the next one thousand years. The one billion people living in acute poverty in the world are those who have the least access to food.

As part of the effort to meet the growing demand for food, fish farming is presently gaining momentum all around the world, with emphasis on aquaculture and dam construction both in fresh water and brackish water (Okpala, 1997). This is part of the stampede provoked by the need to satisfy the 2.500 calories (more precisely kilocalories) which constitute the energy needs of an average person. Energy and protein deficiency are causative to stunted growth, impaired lives, kwashiorkor, and marasmus, which themselves are implicated in the causation of 15 - 20 million deaths per year, and have a prevalence of about 750 million people.
Throughout most of human history, the bodies of water have been related to as a limitless resource. Humans have long relied on fish as an important source of food. In this respect the food yield from fish and sea food in yield was 110 million metric tans. Fish farming, sometimes called the Blue Revolution has the potential to contribute to human food needs. Much of fish farming involves growing fish in enclosures. But the open ocean can also be used for rearing fish. For example salmon that are released into rivers will head out into the oceans where they will live for a number of years. The salmon can then be harvested as they return to the rivers to breed.

However there is an increasing awareness of the importance of disease as one of the major factors detrimental to fish culturing. Fishing industries

suffer great losses each year as a result of disease and parasites. It is gratifying to note that the
shortage of personnel experienced in fish pathology and parasitology is being redressed. Besides the effects of parasites on fish, further set backs encountered in fish production have been traced to many environmental hazards that affect fish both in culture and in their natural environment. These variable conditions of water bodies make fish in culture and lentic environments more susceptible to parasites. As the status of the world's fisheries consequently grows more perilous nations are beginning to cooperate to solve pressing problems. Many countries have reached a number of agreements which if complied with will definitely have a significant and beneficial impact.

Baker (1997) has articulated some of these multilateral solutions and palliatives. Among the most significant is the United Nations Convention on the Law of the Sea UNCLOS, which was drafted in 1982 and made official in 1994. The UNCLOS agreement extended a nations sovereignty to cover fish within 200 nautical miles (370 kilometres) of that nation’s coast, an area known as the Exclusive  Economic Zone. In addition to accepting these borders, nations that signed on to UNCLOS agreed to protect and preserve the marine environment and to adopt laws and regulations to prevent pollution. Another agreement is the United Nations Environment Protection Programme Conference on Protection of the Marine Environment from Land-Based activities, which in 1995 developed an action plan for preventing or reducing pollution from sewage, siltation, industry, logging, and other sources. Without denying the strategic importance of these regulations in ensuring fish food availabilities, it must be observed that only ten percent of the world's catch comes from international waters. The efforts of some nations supplementary to the international conventions are remarkable.

According to Baker (1997), New Zealand has been a pioneer in no-fishing zones, setting aside protected areas where fish can grow and reproduce before they are harvested. In the Philippines the government gives communities 25-­year contracts to manage coastlines with success stories in designating no-fishing zones and limiting fish catches. In 1995 the World

Bank joined with the World Conservation Union and the Great Barrier Reef Marine Park Authority of Australia to map and plan for preserving 155 key marine protection areas affording critical sites of breeding and migration, biological wealth and habitat for endangered species.Yet some of the measures thus far adopted have only amounted to an exercise in futility. For example, the Magnuson Fishery Conservation and Management Act passed in 1976 established the US EEZ as a way to protect US marine resources from foreign fishing fleets and was further supposed to encourage fish conservation. But the US National Fish and Wildlife Foundation, NFWF, reported that by 1990 one-third of the fish stocks being managed were worse off than when the Act was signed.

Not withstanding cases of ineffective regulation, efforts most continue on account of the importance  of fish as a food item.
Fish and humans
It is impossible to overstate the importance of fish to human populations around the world. Historically fish protein has been a food source to man, with wild caught fish providing the bulk of fish protein. According to Orr (2006), recent advances in fish fanning especially with some African cichlids have alleviated hunger in many parts of the world. In industrialized countries, fish from aquacultural activities are a major relief for over fished stocks of wild fish. Fisheries also serve as recreational place for many people. Aquariums, in which are kept mainly minnows, characins and cichlids, are found in more than twenty million homes in the US alone.

Chiefly, fish commands the greatest respect from humans on account of its food value and economic significance generally. Because oceans provide the largest and best habitat for fish, they are being looked to as a major source of food for the future. Estimates of the yearly world ocean production of organic matter, fixed from inorganic carbon and nutrients, amount to about 130 billion metric tons, while yearly harvests amount to about 82 million metric tons of fish. The current yield supplies about 5.6 percent of the protein needs of the world at the present time (Slykind and Wehmiller, 2006). The tabulation below affords more insight into the food relationship between fish and humans.

Table 1:           Fisheries – quantity and value of domestic catch in US
                                  (quantity in million pounds)



Human food

Industrial products

Value($ million)


































































Source: National Marine Fisheries Service, US.

The table above makes it clear that about eighty percent of all domestic fish catch in the US is meant directly to serve as food in homes. The balance is applied industrially as meal, oil fish soluble, homogenized condensed fish, shell products, bait, and animal food. A visible trend in the table is the growth in fish catch from the beginning of the thirteen-year time series up to 1993, which represents the record year. Since then, there has been a secular decline, especially in the proportion meant for consumption as human food, although there was also an increasing trend in commercial catch between 1999 and 2001. It should be noted that the quantity figures are given in terms of live weight.

Table 2: Commercial catch of fish crustaceans, and mollusks by major fishing areas of the world (metric tons)





Inland waters




Marine areas




Pacific ocean




Atlantic ocean




Indian ocean




Source: Food and Agriculture Organisation of the United Nations.

Analysis of table 2 shows that the marine areas, that is the oceans, account for the overwhelming proportion of commercial catch of fish, crustaceans and mollusks. The two tables above go to illustrate how intimately man's food behaviour is related to fish and fisheries. Southeast Asian cuisine is a well respected international delicacy. Yet, a unique feature of this regions cuisine is fermented sea foods, which are prepared by the action of micro-organisms that chemically change the foods flavour and appearance. Varieties of fish sauce and pungent shrimp paste are used as flavourings and condiments.

Even macrobiotics permit a good deal of fish diet. Macrobiotics is diet based on whole grains beans and vegetables that incorporates many traditional Japanese foods as well as far Eastern philosophy into an overall lifestyle that seeks harmony and balance for body, mind, and spirit. The macrobiotic diet is not strictly vegetarian; lean fish and other sea food are eaten occasionally. On the whole, fish are an important source of protein for millions of people worldwide. Since the early 1970s, 70 to 100 million metric tons of fish are caught each year for food as shown in tables I and 2. Fish protein represents about 25 percent of the total animal protein consumed by the world's population, second only to beef. But parasites continue to pose a serious threat to fish availability for man's use.

Parasites of fish

Each true fish parasite uses the fish host for its house and food. Long ago it was pointed out that the understanding of the relationship between fishes, their environment, pathogens and parasites is very important in fish culture and forms the basis for rational management (Sniezko, 1974). Parasites occasion diseases which in addition to killing the host fish can materially reduce the value of the fish to humans as food. Bauer et al (1981) the stressed the fact that parasitic infection in fishes usually increase

when fishes are reared in artificial conditions. According to Kabata (1995), fish parasites can get into your pond by introducing fish without a proper quarantine period and examination. They can also hitch a ride on water plants, snails, frogs and birds.

Symptoms of parasitic infection

Jordan (2005) stated that heavily infested fish will show various signs of stress. They might scrape themselves against the sides or bottom of the pond repeatedly. In serious infestations fish will rub areas on their skin or fins raw and develop skin and fin infections. Sometimes they will just act funny or suspend at an odd angle in the water. They might even jump out of the water. Sometimes the opposite is true. Fish will lie on the bottom with fins tightly clamped to their bodies. They can either be extra slimy showing a whitish film or almost lacking a slime coat. They can have irritated reddish sports or streaks on their backs sides or bellies (Amos, l985). You cannot diagnose which parasite you have by the symptoms. Therefore identify the type of parasite in your fish pond and treat them specifically and effectively. In some cases there may be more than one type found.

Below is a schematic and simplified presentation of symptoms, causes and treatment of certain parasitic infections of fishes.





Treatment and Links

A).   Fish gasp for air at the top of the water.  They sometimes flash, or jump.  They rub on rocks or other objects.  Gills may be bleeding.

Fish Behavioral Disorders Flow Chart

Gill Flukes (Dactylogyrus)

Fish Behavioral Disorders Flow Chart

Treat with: De-Los and use  Koi Fix® if the fish develop any secondary infections after the flukes are gone

If not, look down the chart further

B).   The fish have small pimples on the skin, or reddened areas with a white thread-like worm sticking out.

Fish Behavioral Disorders Flow Chart

Anchor Worm (Lernaea)

Fish Behavioral Disorders Flow Chart

Treat with: De-Los

If not, look down the chart further

C).   Small, round, clear to whitish objects are stuck all over the fish.  The fish flash and scratch

Fish Behavioral Disorders Flow Chart

Fish Lice (Argulus)
Mites (Hydrachnellae)

Fish Behavioral Disorders Flow Chart

Treat with: De-Los

If not, look down the chart further

D).  Small thin to fatter brown objects are stuck all over my koi

Fish Behavioral Disorders Flow Chart

The fish are infested with leeches
(Placobdella montifera)

Fish Behavioral Disorders Flow Chart

Treat with:  De-Los

If not, look down the chart further

E).   The fish have small clear/white worm-like objects stuck to their skin

Fish Behavioral Disorders Flow Chart

Skin Flukes (Gyrodactylidiasis)

Fish Behavioral Disorders Flow Chart

Use: De-Los

If not, look down the chart further

F).  My fish are breathing heavily, have a heavy slime coat, and appear to have round, flat parasites on them

Fish Behavioral Disorders Flow Chart

Your fish is affected by Trichodina

Fish Behavioral Disorders Flow Chart

Treat the fish with Forma-Green

If not, look down the chart further

G).  My fish have swollen bellies, even though they have not been fed for a couple of days.  They seem to eat normally, or are very hungry.

Fish Behavioral Disorders Flow Chart

Three items can cause this:
a). Mitospora (acites, severe bloating, pineconed scales)
b). Capillaria (clear feces?)
c). Tapeworm

Fish Behavioral Disorders Flow Chart


a). No suitable treatment.
b). Paracide-D
c). Paracide-D


Source: ©1995-2006 - Site Map - Site Design by Brian Aukes & AFAM LLC.

Types of fish parasite
The fish parasite that can be seen without a microscope is the Anchor worm and fish lice which attach themselves to fish body and by breaking the skin can cause an infection. Jordan (2005) described fish lice (Argulus)as small crustaceans that attach themselves to fish skin. Fish lice are about the size of your small finger nail but clear and blend with the fishes skin.

Anchor worms (Lernea elegans) attach themselves under a fish scale. Full size adults are one half to three fourths ofan inch long and are quite easy to see. The Acanthocephalans live as adults in the intestines of vertebrates, most of which are fishes (Nnadi, 2005). Microscopic fish parasites include the flukes and the protozoans. The flukes are tiny flat worms found on the skin of fish as well as around their gills. Flukes rarely kill fish but they are known to be a major contributor to fish disease.
The protozoans are more tiny than the flukes, and are more deadly to fish. The protozoans include:
i)          The ich: which is a very dangerous parasite that will attack every fish in the pond regardless of health.
ii)         Costia: which can quickly overwhelm and kill your fish. Costia parasites inject toxins into the gills and skin, digest tissues and allow bacterial infections to begin.
iii)        Chilodonella: This is somewhat less deadly than ich or costia.
iv)        Trichodina:This is least deadly of the protozoans and usually found in dirty ponds with high        organic matters.

Place any fish suspected to have parasites in a plastic bag and look at them very closely. If you see red spots or areas that look irritated scrape gently and apply a small disinfectant. In case of fish lice scraping can be done with finger nails. For the Anchor worms a pair of tweezers is used to pull them gently off fish body.

The flukes are easy to  find using microscope at low power about 40x and the protozoans are viewed at medium (100x) to high power (400x ). In order to see and identify them they must be alive, motile, and swimming around on the slide.


The cure for fish lice and anchor worms is easy but hard to obtain. The best product is dimilin which is a gyrase inhibitor that is added directly to the pond. It is nontoxic to fish and kills fish lice and anchor worms within three to four days. Because of the different types of parasites involved, treatment must be with specificity. When multiple parasites are present treatment must be sequential and in multiples to eradicate them all. After any treatment, fishes should be reexamined to be certain all parasites have been eliminated successfully (Jordan, 2005).

Prevention is always the best approach to control parasitic infections. Buy only good quality, compatible fish: Quarantine new fish before adding them to the aquarium. Avoid stressing the fish with rough handling and sudden changes in conditions. Do not overfeed your fish, remove sick fish to a hospital tank for treatment, disinfect nets used to move sick fish, do not transfer water from the quarantine tank to the main aquarium, and do not let any metal come in contact with the aquarium water.


This paper has revealed the trauma of fish parasites and the huge cost to fish industry. It is recommended that all new plants added to the ponds be treated with formalin for at least two weeks before placing in the ponds. Ponds should be designed to keep frogs and birds away.


Amos, K.H, (ed) (1985) Procedure for the detection and identification of certain fish pathogens. 3rd ed. Fish Health section, American Fisheries Society, Corvallis. Oreg. 114pp.

Baker, B. (1997): Falling fish stocks, Encarta Yearbook. February.

Baner, O.N; Egusa, S., and Hoffman, G.L. (1981): Parasitic infections of economic importance in fishes. Review of  advances in fish parasiology; Warszawa. Japan pp425-443.

Jordan, R. (2005) Fish parasites 101 http: 1164.232.
Kabala, Z. (1985) Parasites and disease: of fish cultured in the topics, Philedephis: Taylor and Francis

Klinger, R. E. and Francis- Floyd, R.(2002): Introduction to Freshwater Fish Parasites CIR716, one of a series of the Fisheries and Aquatic Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.

Nnadi, E. I.  (2005) Elements of Parasitology, Owerri, Nigeria: Reliable Publishers..


Okpala, E.I (1997) Studies on the parasitic infection of fishes in the Rurnuji and New Calabar Rivers of Rivers State (unpublished) MSc thesis  submitted to University of Port Harcourt

Orr,  J.W. (2006): Fish and humans. Encarta  Encyclopedia

Skylind, E.B. and Wehmiller, J.F. (2006)' Ocean and oceanography, Encarta  Encyclopedia.

Silleszko, S.F. (1974): The effect of environmental stress on outbreak of infectious diseases of fish. Journal of fish biology Vol (. pp 197 - 208