FISH PARASITES, FISH FOOD, AND THE MARINE ENVIRONMENT
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.
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
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.
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
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)
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.
Types of fish parasite
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 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).
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.
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