Feeding enzymes to shrimp and fish in Sustainable Aquaculture

Commercial fish feeds usually contain high fish meal as the major protein source, ranging from 30-50 per cent (Hardy, 1995). But now-a-days, fish meal is generally avoided in the feed due to its scarcity and high cost. Hence, aquaculture nutrition have been trying to improve the nutritional value of fish feed by enzyme supplementation, to find suitable alternatives to fish meal, since last decades, stated Prakash Chandra Behera, Technical Manager of AQUA, PVS Group, India.

Feeding enzymes to shrimps and fishes is one of the major nutritional advances in the aquaculture sector since last few years. Exogenous enzymes are now extensively used throughout the world as additives in animal diets. Also, supplementation with enzymes can help to eliminate the effects of antinutritional factors and improve the utilization of dietary energy and amino acids, resulting in improved performance of fish/shrimps (Farhangi and Carter, 2007; Lin et al., 2007; Soltan, 2009).

The primary purpose of enzyme application in feeds is to improve digestion. The digestive processes will work better and result shown in improved feed efficiency by providing an extra dose of enzymes. Further, aquatic animals are lack certain digestive enzymes during early development or throughout their life. In the case of fishes / shrimps lacking certain enzymes even in adulthood, application of these enzymes results in better utilization of nutrient fractions that are digested by the enzymes.


Enzymes are one of the many types of protein in biological systems. Their primary characteristic is to catalyze the rate of a reaction but is not themselves altered by it. They are involved in all types of anabolic and catabolic pathways of digestion and metabolism. Enzymes tend to be very specific catalysts that act on one or ,at most a limited group of compounds known as substrates. Enzymes provide additional powerful tools that can inactivate anti-nutritional factors and enhance the nutritional value of plant-based protein in feeds. They provide a natural way to transform complex feed components into absorbable nutrients.

The addition of enzymes in feed can improve nutrient utilization , reducing feed cost and the excretion of nutrients into the environment.

Sources of Enzymes:

Enzymes are produced in every living organisms from the higher animals and plants to the simplest unicellular forms of life as they are essential for metabolic process. Microorganisms that generally involved in production of various enzymes are:

Bacteria: Bacillus subtilis, Bacillus lentus, Bacillus amyloliquifaciens and Bacillus stearothermophils.

Fungus: Triochoderma longibrachiatum, Asperigillus oryzae , Asperigillus niger and yeast

Microbial enzymes

In animals, digestion of food is carried out by the animal’s digestive system and by microorganisms that inhabit the intestinal tract. The bacteria present in the gastrointestinal tract of fish/shrimp are potent producers of proteolytic enzymes. They may also produce cellulase moderately. The adding of live microorganisms to diets to produce enzymes is possible in specialty feed applications. Large scale commercial enzyme applications are rely on enzymes produced by microbial fermentation technology.

Anti Nutritional Factors in Aquafeed

Feed ingredients from plants sources contain some compounds that either the shrimp/fish cannot digest or which hinder its digestive system because they cannot produce the require enzymes to degrade .Though the palatability of many plant materials has demerits, anti-nutritional factors are the most serious concern in replacing the fishmeal completely in feed formulations. Anti-nutritional factors have an adverse impact on the digestion of feed and its efficiency. There are many kinds of anti-nutritional factors and they are associated with the most widely used plant materials like trypsin inhibitor proteins, glucosinolates and phytate.

Heat inactivation and water soaking are the two common detoxification methods used to overcome most of the anti-nutritional factors.

Factors contributing to use of Enzymes

  • Increase need for quality food grain for fish/shrimp
  • Increase need for quality animal products /by –products
  • Search for alternate sources of food with better nutritive value
  • Economic margins(reduced cost : benefit cost)
  • Quick realization of profits
  • Rise of environmental awareness

Types of Enzymes available for Fishes / shrimps

Many enzymes have been used in fish/shrimp nutrition over the past several years which includes cellulose, (β-glucanases), xylanases and associated enzymes like; phytase, proteases, lipases and galactosidases. Enzymes in the feed industry have mostly been used for culture animals to neutralize the effects of the viscous, nonstrach polysaccharides in cereals and other food grains.

Action & Benefits of Feed Enzymes:

  • Reduces in digesta viscosity
  • Enhances digestation and absorption of nutrients especially fat & protein.
  • Improves Apparent Metabolizable Energy(AME) value of the diet
  • Increases feed intake, weight gain and feed gain ratio
  • Reduces ammonia production
  • Improves nutrient Digestibility.

Endogenous enzymes found in the fish/shrimp digestive system which help to break down large organic molecules like starch, cellulose and protein into simpler substances.

The carbohydrate digestion improves by using microbial enzymes. Addition of exogenous carbohydrates enzymes to feed increase utilization of unavailable dietary carbohydrates .High levels of non-starch polysaccharides (NSP) such as cellulose, xylans and mannans reduce the nutritive value of many plant ingredients. Intestinal enzymes to digest these carbohydrates are not produced by most animals.

[Read more at thefishsite]

Algae as Alternatives to Fishmeal in Fish Feeds

Why algae?

The reader may wonder why algae, including both macroalgae (‘seaweeds’) and microalgae (e.g. phytoplankton), and which are popularly thought of as ‘plants’, would be good candidates to serve as alternatives to fishmeal in fish feeds. One fundamental consideration is that algae are the base of the aquatic food chains that produce the food resources that fish are adapted to consume. But often it is not appreciated that the biochemical diversity among different algae can be vastly greater than among land plants, even when ‘Blue-Green Algae’ (e.g. Spirulina), more properly called Cyanobacteria, are excluded from consideration. This reflects the very early evolutionary divergence of different algal groups in the history of life on earth. Only one of the many algal groups, the Green Algae, produced a line of descent that eventually gave rise to all the land plants.Therefore it can be difficult to make meaningful generalisations about the nutritional value of this extremely diverse group of organisms; rather it is necessary to consider the particular qualities of specific algae.

Protein and amino acids

Fishmeal is so widely used in feeds largely thanks to its substantial content of high-quality proteins, containing all the essential amino acids. A critical shortcoming of the crop plant proteins commonly used in fish feeds is that they are deficient in certain amino acids such as lysine, methionine, threonine, and tryptophan (Li et al. 2009), whereas analyses of the amino acid content of numerous algae have found that although there is significant variation, they generally contain all the essential amino acids. For example, surveys of 19 tropical seaweeds (Lourenço et al. 2002) and 34 edible seaweed products (Dawczynski et al. 2007) found that all species analysed containedall the essential amino acids, and these findings are consistent with other seaweed analyses (Rosell andSrivastava 1985, Wong and Peter 2000, Ortiz et al. 2006).

Analyses of microalgae have found similar high contents of essential amino acids, as exemplified by a comprehensive study of 40 species of microalgae from seven algal classes that found that, “All species had similar amino acid composition, and were rich in the essential amino acids” (Brown et al. 1997).


One often-overlooked nutrient is the non-protein sulphonic acid taurine, which is sometimes lumped with amino acids in discussions of nutrition.Taurine is usually an essential nutrient for carnivorous animals, including some fish, but it is not found in any land plants. However, although taurine has been much less often investigated than amino acids, it has been reported in significant quantities in macroalgae such as Laminaria, Undaria, and Porphyra (Dawczynski et al. 2007, Murata and Nakazoe 2001) as well as certain microalgae, for example the green flagellate Tetraselmis (Al-Amoudia and Flynn 1989), the red unicellular alga Porphyridium (Flynn and Flynn 1992), the dinoflagellate Oxyrrhis (Flynn and Fielder 1989), and the diatom Nitzschia (Jackson et al. 1992).


A few algae are used as sources of pigments in fish feeds. Haematococcus is used to produce astaxanthin, which is responsible for the pink colour of the flesh of salmon. Spirulina is used as a source of other carotenoids that fishes such as ornamental koi can convert to astaxanthin and other brightly coloured pigments. Dunaliella produces large amounts of beta-carotene.


In addition to its high content of high-quality protein, fishmeal provides lipids rich in ‘PUFAs’, or polyunsaturated omega-3 and omega-6 fatty acids. These are the ‘fish oil’ lipids that have become highly prized for their contribution to good cardiovascular health in humans. But it is not always appreciated that algae at the base of the aquatic food chain in fact originate these ‘fish oil’ fatty acids.These desirable algal fatty acids are passed up the food chain to fish, and they are indeed essential nutrients for many fish.

Algae have been recognised as an obvious alternative source of these ‘fish oil’ fatty acids for use in fish feeds (Miller et al. 2008), especially eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (ARA). There is a substantial literature devoted to analysis of the PUFA content of microalgae, particularly those used in aquaculture, because they have long been recognised as the best source of these essential nutrients for production of zooplankton necessary for the first feeding of larval fish, as well as filter-feeding shellfish.

Many shellfish producers are aware the sterol profile of feed lipids is of critical importance, but much less attention has been paid to the importance of the sterol profile of fish feeds. Aside from alterations in the normal sterol profile of the fish, the possible endocrine effects of plant phytosterols in fish feeds (e.g. soy phytohormones) have yet to be thoroughly investigated (Pickova and Mørkøre 2007).

[Read more on Use of algae in formulated fish feeds & Choosing the right algae at thefishsite]

Ammonia in Fish Ponds

Ammonia is toxic to fish if allowed to accumulate in fish production systems. When ammonia accumulates to toxic levels, fish cannot extract energy from feed efficiently. If the ammonia concentration gets high enough, the fish will become lethargic and eventually fall into a coma and die.

In properly managed fish ponds, ammonia seldom accumulates to lethal concentrations. However, ammonia can have so-called “sublethal” effects—such as reduced growth, poor feed conversion, and reduced disease resistance—at concentrations that are lower than lethal concentrations.

Source of ammonia

The main source of ammonia in fish ponds is fish excretion. The rate at which fish excrete ammonia is directly related to the feeding rate and the protein level in feed. As dietary protein is broken down in the body, some of the nitrogen is used to form protein (including muscle), some is used for energy, and some is excreted through the gills as ammonia. Thus, protein in feed is the ultimate source of most ammonia in ponds where fish are fed.

Another main source of ammonia in fish ponds is diffusion from the sediment. Large quantities of organic matter are produced by algae or added to ponds as feed. Fecal solids excreted by fish and dead algae settle to the pond bottom, where they decompose. The decomposition of this organic matter produces ammonia, which diffuses from the sediment into the water column.

Ammonia management options

Stop Feeding or Reduce Feeding Rate

The primary source of nearly all the ammonia in fish ponds is the protein in feed. When feed protein is completely broken down (metabolized), ammonia is produced within the fish and excreted through the gills into pond water. Therefore, it seems reasonable to conclude that ammonia levels in ponds can be controlled by manipulating feeding rate or feed protein level. This is true to some extent, but it depends on whether you want to control it over the short-run (days) or the long-run (weeks or months).

In the short-run, sharp reductions in feeding rate have little immediate effect on ammonia concentration. The ecological reason for this is based on the complex movement of large amounts of nitrogen from one of the many components of the pond ecosystem to another. In essence, trying to reduce ammonia levels by withholding feed can be compared with trying to stop a fully loaded freight train running at top speed—it can be done but it takes a long time.

Producers can reduce the risk over the long-run by adjusting both feeding rate and feed protein level. Limit feed to the amount that will be consumed. In mid-summer the maximum daily feeding rate should be 100 to 125 pounds per acre. By feeding conservatively, the potential for high ammonia in ponds and the risks associated with sub-lethal exposure (disease, poor feed conversion, slow growth) can be minimized.

Increase Aeration

The toxic form of ammonia (NH3) is a dissolved gas, so some producers believe pond aeration is one way to get rid of ammonia because it accelerates the diffusion of ammonia gas from pond water to the air. However, research has demonstrated that aeration is ineffective at reducing ammonia concentration because the volume of water affected by aerators is quite small in comparison with the total pond volume and because the concentration of ammonia gas in water is typically fairly low (especially in the morning). Intensive aeration may actually increase ammonia concentration because it suspends pond sediments.

Add Lime

It has long been thought that liming ponds decreases ammonia concentrations. In fact, using liming agents such as hydrated lime or quick lime could actually make a potentially bad situation much worse by causing an abrupt and large increase in pH. Increasing pH shifts ammonia toward the form that is toxic to fish. In addition, the calcium in lime can react with soluble phosphorus, removing it from water and making it unavailable to algae.

In ponds with similar algal density, daily fluctuations of pH in lowalkalinity pond waters are more extreme than those in waters of sufficient alkalinity (greater than 20 mg/L as CaCO3; see SRAC Publication No. 464). Therefore, liming can moderate extreme pH values, particularly those that occur during late afternoon when the fraction of total ammonia that is in the toxic form is highest. However, this technique is effective only in ponds with low alkalinity. Most fish ponds have sufficient alkalinity. Increasing the alkalinity above 20 mg/L as CaCO3 will not provide additional benefit. Furthermore, liming does not address the root causes of high ammonia concentration; it only shifts the distribution of ammonia from the toxic to the non-toxic form by moderating high pH in the afternoon.

Fertilize with Phosphorus

Most of the ammonia excreted by fish is taken up by algae, so anything that increases algal growth will increase ammonia uptake. This fact is the basis for the idea of fertilizing ponds with phosphorus fertilizer to reduce ammonia levels. However, under “normal” pond conditions, algae blooms in fish ponds are very dense and the rate of algae growth is limited by the availability of light, not nutrients such as phosphorus or nitrogen. Therefore, adding phosphorus does nothing to reduce ammonia concentration because algae are already growing as fast as possible under the prevailing conditions.

The highest ammonia concentrations in fish ponds occur after the crash of an algae bloom. Fertilization, particularly with phosphorus, may accelerate the re-establishment of the bloom, but most ponds have plenty of dissolved phosphorus (and other nutrients) to support a bloom and do not need more.

Reduce Pond Depth

Algal growth (and therefore the rate of ammonia uptake by algae) in fish ponds is limited by the availability of light. Anything that increases light increases ammonia uptake. Theoretically, dense algae blooms in shallow ponds will remove ammonia more effectively than the same dense blooms in deeper ponds. On balance, however, there are probably more benefits associated with deeper ponds (e.g., ease of fish harvest, water conservation, more stable temperatures, reduced effect of sedimentation on interval between renovations).

Increase Pond Depth

 Obviously, deeper ponds contain more water than more shallow ponds. Therefore, at a given feeding rate, deeper ponds should have lower ammonia concentrations because there is more water to dilute the ammonia excreted by fish. In reality, deeper ponds do not usually have enough water to significantly dilute ammonia when compared to the large amounts of ammonia in constant flux between various biotic and abiotic compartments in ponds. Furthermore, deeper ponds are more likely to stratify and the lower layer of pond water (the hypolimnion) can become enriched with ammonia and depleted of dissolved oxygen. When this layer of water mixes with surface water in a “turnover,” severe water quality problems may result.

Flush the Pond with Well Water

 Ammonia can be flushed from ponds, although pumping the huge volume of water required to do so in large commercial ponds is costly, time-consuming and unnecessarily wasteful. It is also deceptively ineffective as an ammonia management tool. For example, assume the ammonia concentration in a full, 10-acre pond is 1 mg/L. The ammonia concentration after pumping 500 gpm continuously for 3 days (equivalent to about 8 inches of water) will be 0.90 mg/L, a drop of only 0.10 mg/L.

Instead of simply running water through a pond as in the example above, now assume that about 8 inches of water is discharged from the pond before refilling with well water. In this case, the decline in ammonia concentration will be slightly greater (to 0.83 mg/L), but even this decrease is not enough in an emergency situation, particularly when the extra time needed to drain the water before refilling is considered. The difference in the two flushing scenarios is related to the blending of pond water with pumped water before discharge in the first case.

Just as paddlewheel aeration creates a zone of sufficient dissolved oxygen concentration, pumping groundwater creates a zone of relatively low ammonia concentration adjacent to the water inflow. The effectiveness of this practice is questionable because it does not address the root cause of the problem and wastes water. Flushing ponds is not only ineffective, but highly undesirable because of concerns about releasing pond effluents into the environment.

Add Bacterial Amendments

 Common aquatic bacteria are an essential part of the constant cycling of ammonia in a pond ecosystem. Some people believe that ammonia accumulates in ponds because the wrong kind or insufficient numbers of bacteria are present. If this were true, adding concentrated formulations of bacteria would address the problem. However, research with many brands of bacterial amendments has consistently given the same result: Water quality is unaffected by the addition of these supplements.

Standard pond management creates very favorable conditions for bacterial growth. Bacterial growth and activity is limited more by the availability of oxygen and by temperature than by the number of bacterial cells. Also, the most abundant type of bacteria in many amendments (and in pond water and sediment) is responsible for the decomposition of organic matter. Therefore, if bacterial amendments accelerate the decomposition of organic matter, ammonia concentration would actually increase, not decrease.

Another kind of bacteria in amendments oxidizes ammonia to nitrate. Adding them will not reduce the ammonia concentration rapidly because the bacteria must grow for several weeks before there is a large enough population to affect ammonia level.

Add a Source of Organic Carbon

 If the dissolved oxygen concentration is adequate, adding a source of organic carbon, such as chopped hay, to intensive fish ponds can reduce ammonia concentration. Many bacteria in fish ponds are “starved” for organic carbon, despite the addition of large amounts of feed. Organic matter in fish ponds (dead algae cells, fish fecal solids, uneaten feed) does not contain the optimum ratio of nutrients for bacterial growth. There is more than enough nitrogen for bacterial growth so the excess is released to the pond water.

Adding organic matter with a high concentration of carbon relative to nitrogen promotes the “fixation” or “immobilization” of the ammonia dissolved in water. Incorporating ammonia into bacterial cells packages the nitrogen into a particulate form that is not toxic to fish. The down side of this approach is that it is hard to apply large amounts of organic matter to large ponds and the effect on ammonia concentration is not rapid. Furthermore, aeration will have to be increased to address the demand for oxygen by large quantities of decomposing organic matter.

Add Ion Exchange Materials

 Certain naturally occurring materials, called zeolites, can adsorb ammonia from water. These are practical to use in aquaria or other small-scale, intensive fish-holding systems, but impractical for largevolume fish ponds.

Some shrimp farmers in Southeast Asia have tried making monthly applications of zeolite at 200 to 400 pounds per acre. However, research has demonstrated that this practice is ineffective at reducing ammonia concentration in ponds and it has now been abandoned.

Add Acid

 In theory, adding acid (such as hydrochloric acid) to water will reduce pH. This can shift the ammonia equilibrium to favor the non-toxic form. However, a large amount of acid is necessary to reduce the pH in well-buffered ponds and it would have to be mixed rapidly throughout the pond to prevent “hot spots” that could kill fish. Furthermore, adding acid would destroy much of the buffering capacity (alkalinity) of the pond before any change in pH could occur. Once the ammonia concentration is lowered, treated ponds might require liming to restore the buffering capacity. Working with strong mineral acids is a safety hazard for farm workers and for fish.

[Source: thefishsite.com]

Parasitic Diseases of Tropical and Ornamental Fish

Fish can serve as an intermediate, transport and/or definitive host for the various parasites. As a result, parasites can be found infesting the outer skin surfaces, inhabiting the lumen of any organ, or deeply embedded within the parenchyma of any tissue of the host. Parasitic infections in fish are diagnosed by direct observation, wet mount preparations of skin, gill and fins, fecal samples, tissue squashes, blood smears, and histopathology.

External protozoan parasites

Numerous protozoan parasites penetrate the epithelial tissues of the skin and gills of fish. Perhaps the most readily recognized protozoan fish parasite is Ichthyophthirius multifiliis, commonly referred to as “Ich” or “white spot disease”. This large parasite causes multiple small raised, white lesions that develop as a result of the parasite residing in the skin, fins and gill tissue of the host. The parasite is covered with an external surface layer of cilia and can be identified by the presence of a relatively large horseshoe-shaped or C-shaped macronucleus. Cryptocaryon irritans is the saltwater equivalent of the freshwater Ichthyophthirius organism and causes similar clinical signs. This parasite is another relatively large ciliate, but does not have the large C-shaped nucleus that is characteristic of Ichthyophthirius. Another ciliate that occasionally causes problems by invading the deeper tissues of fish is Tetrahymena pyriformis. This parasite causes “tet” or “guppy disease” in a number of species of tropical aquarium fishes, especially guppies, neon tetras and mollies. The small, cylindrical-shaped organism penetrates the epithelial tissues and continues migrating along the fascial planes of the underlying muscles to invade many of the internal organs.

Many fish parasites do not actually invade the tissues, but feed off the mucus, bacterial and sloughed epithelial cells on the surface, or have attachment organs that anchor the parasite in place on the surface of the skin and feed on bacterial, protozoan and other material in the passing water. Of the protozoans that infest the surface of the skin of fish is a group of flattened, discoid ciliates of the genera Trichodina, Trichodinella and Tripartiella. These parasites of freshwater, brackish and marine species are readily identified by their internal circular denticular ring that has both an inward and outward facing ring of tooth-like projections. Those that parasitize the gill are generally most pathogenic where they cause significant tissue irritation, hyperplasia of epithelial tissues and respiratory problems. Chilodonella sp. is a dorsoventrally flattened, oval protozoan that has cilia located in distinct bands along the surface of the body. This freshwater parasite causes irritation of the gills and fins by its feeding activity which results in hyperplasia and fusion of gill lamellae and hyperplasia of fin tissue. Ichthyobodo sp. (~ Costia sp.) is an extremely small pyriform-shaped flagellate of freshwater fish. This parasite can be found either attached by one of its two flagella to the skin and gill tissues or in the water displaying a characteristic spiraling swimming behavior.

A diverse group of ciliated parasites that attach directly to the skin of the fish and do not actually feed on the fish but obtain food from the water as it passes by the fish. These include Ambiphyra sp., Trichophyra sp., Epistylis sp. and Heteropolaria sp., all of which have a disk for attaching to the surface of the epithelial cells of the skin or gill. Though these parasites do not normally cause a problem in small numbers, the health of the fish can be affected if large numbers of the parasites are present on the gills where they can disrupt diffusion of respiratory gasses and excretory products.

Dinoflagellates of the genera Piscinoodinium (Oodinium), Amyloodinium, and Crepidoodinium are parasitic on freshwater and marine species of fish. These parasites cause a disease commonly called “velvet disease” or “rust disease” due to the reddish coloration the parasites impart to the affected body, fins or gills. The parasite has finger-like projections (rhizoids) that penetrate the epithelial cells and act as holdfast organs and obtain nutrients from the cells. Infestations of the gill tissue cause epithelial hyperplasia and fusion of the lamellae resulting in secondary hypoxia and osmoregulatory compromise.

Internal protozoan parasites

Spironucleus sp. and Hexamita sp. are small flagellate parasites that are frequently found in the lumen of the intestinal tract of freshwater and marine tropical fish. Mild infestations of the intestinal tract are generally asymptomatic, while heavy infestations can be pathogenic causing necrosis and sloughing of the intestinal epithelium. The resulting clinical signs include inappetence, unthriftiness, mucoid or pale stool, poor condition, emaciation and death.

Microsporidean parasites (now classified with the fungal organisms) produce a spore-filled cyst within almost any tissue of many freshwater and marine species. As the cysts gets larger, infected muscle tissue becomes displaced and turns white in color. Pleistophora hyphessobryconis, causes a syndrome called “neon tetra disease” in zebra danios, cichlids and cyprinids. Myxosporideans are a common sporozoan parasite of many species of fish. These parasites form a spore-filled tissue cyst that displaces or disrupts the function of the infected tissue.

Coccidial (Eimeria sp. and Goussia sp.) infections of the intestinal tract and kidney, respectively, are a common occurrence in young fish where infection can cause poor growth, emaciation and death. Infections can also be found in adult fish, but the resulting pathology is generally less severe.

Both freshwater and marine fishes have a number of flagellated hemoprotozoans that can cause health problems. Trypanosoma sp. has be described from the blue-eyed plecostomus (Panaque suttoni) imported from South America, while Cryptobia iubilans has been described as causing a granulomatous disease in African cichlids and discus.

Helminth Parasites

Monogeneans are parasitic flatworms that infest the external surfaces of many species of freshwater, brackish or marine fish. The monogeneans have an anterior oral sucker used for feeding on mucus and sloughed epithelial cells, while the posterior end has a holdfast organ for attaching to the host. These parasites cause focal irritation, increased mucus production and hyperplasia of the epithelial tissues due to their the feeding activity around the central point of attachment.

Many species of trematodes, cestodes, nematodes and acanthocephalans use fish as an intermediate host for the developing parasites. These larval stages generally cause minimal pathology, but heavy infestations can result in tissue or organ displacement, stunted growth, and emaciation. Fish can also serve as a definitive host, and can harbor a variety of adult digenetic trematodes, cestodes, nematodes and acanthocephalan parasites in the lumen of their intestinal tracts. As in mammals, these helminthes generally cause minimal pathology in the host fish, though heavy infestations can cause poor growth and emaciation.

Crustacean parasites

A number of crustacean parasites infect the skin and gills of tropical and ornamental fishes. Lernaea sp, or “anchor worm”, is a copepod crustacean of pond-reared fish, especially goldfish, carp and koi. The adult female parasite develops an anchor-shaped anterior end that is embedded in the muscle of the fish, while the posterior portion of the female’s body hangs along the outside of the fish. Ergasilus sp. is a copepod parasite in which the antennae are modified into specialized pincers used to grasp onto the gill filaments of pond and ornamental fish. The “fish louse”, Argulus sp., is a crustacean parasite of many species of pond and ornamental fish. This dorsoventrally-flattened, oval parasite has eight short legs, a dorsal carapace covering the body, two ventrally-located circular sucking discs, two dark eyespots, and a ventral piercing stylet for feeding. This parasite causes a severe inflammatory reaction at the site of stylet penetration and has been implicated in the transmission of several bacterial, viral and hemoprotozoal diseases. Leeches will also occasionally infest ornamental and pond species of fish. Though generally not associated with any significant pathology, large numbers of leeches on an individual can sometimes cause severe anemia and death.


Treatment of the external parasites is fairly simple since most are susceptible to various water-borne chemotherapeutic compounds such as salt, formalin or copper, but treatment of the internal parasites can be difficult to impossible. In addition to the use of chemotherapeutic agents for the treatment of parasites, good husbandry practices are essential for reducing further parasite infestations.


How brown trout tolerate heavily polluted water

New research from the University of Exeter and King’s College London has shown how a population of brown trout can survive in the contaminated waters of the River Hayle in Cornwall where metal concentrations are so high they would be lethal to fish from unpolluted sites.

The team believe this is due to changes in the expression of their genes. The research was funded by NERC and the Salmon and Trout Association.

The researchers compared the trout living in the River Hayle with a population living in a relatively clean site in the River Teign. The results showed that the accumulation of metals in the kidney and liver – where metals are stored and detoxified – were 19 and 34 times higher in the  Hayle trout, respectively. In the gill, concentrations averaging 63 times higher were present in the Hayle fish, but there were no differences in metal content in the gut. This accumulation of metals in the Hayle fish highlights their extraordinary tolerance of the extreme metal concentrations in their environment.

In order to investigate how the Hayle brown trout are able to tolerate such high levels of metal exposure, and also look for potential signs of toxicity, advanced high throughput sequencing was conducted at the Exeter Sequencing Facility to sequence the genes and then measure changes in their expression between the two river sites. The gene encoding a protein, metallothionein, responsible for binding, storing and detoxifying a number of metals, was found to be highly expressed in the River Hayle trout, indicating its importance in their ability to tolerate metals in their environment. Evidence of the presence of other metal-binding and transporting proteins, particularly those responsible for handling iron, was also found.

Usually metals cause toxicity in fish by causing oxidative damage and disrupting the balance of ions in the body. The team found evidence that to counter this toxicity, Hayle fish showed changes in genes responsible for maintaining the balance of these ions in the body and a modest increase in anti-oxidants.

This work was led by T. Uren Webster, Dr R. van Aerle and Dr E Santos from the University of Exeter and Dr N Bury from King’s College London, and has been published in the journal Environmental Science & Technology.

Tamsyn Uren Webster said: “The work demonstrates that this population of brown trout has developed strategies for dealing with the metal pollution in the water and accumulation in their tissues avoiding the lethal damage that such concentrations of metals would normally cause.”

A detailed understanding of how the Hayle trout population has developed this tolerance could have potential implications for re-stocking rivers and increasing food security in polluted regions of the world.

Dr Eduarda Santos from Biosciences said: “The story of the brown trout in the river Hayle is a fascinating one, demonstrating its resilience and its ability to defeat the odds and tolerate the challenges imposed upon them as a result of human activities. Many aspects of this story remain untold: we do not know how or when this tolerance has arisen, and, most importantly, we do not know what the future holds for them if they are challenged with further stressors in their environment. But we know that such populations need careful management; if the Hayle brown trout, with their unique physiology, were to be lost, it is possible that this river may never be home to brown trout again. Therefore, understanding the relationship of fish with their environment is a crucial requirement to effectively manage and protect our aquatic ecosystems.” 

Dr Nic Bury said: “Cornwall has a rich history of mining activity. Despite the cessation of the majority of this activity in the 19th and 20th centuries a number of rivers and estuaries, still possess elevated metals. Brown trout are extremely sensitive to metals when tested in the laboratory. However, biology is remarkable and adaptable, and it is astonishing that trout are able to survive and flourish in the river Hayle. It may be that this population is unique and an important component of the genetic diversity of brown trout.”

[Source Article]

ImageBrown trout   (Photo credit: http://www.fishandboat.com)

How Mussels Cling to Surfaces

By Denise Chow, Staff Writer
When mussels dangle from marine surfaces, they hold on by a cluster of fine threads. These filaments may appear flimsy, but they can actually withstand powerful impacts from currents or crashing waves. Now, researchers are unraveling the secret of these thin, bungeelike cords in order to develop more effective glues and other synthetic biomedical materials.

Unlike barnacles, which fasten themselves tightly to rocks or piers, mussels use silky fibers, called byssus threads, to loosely attach to a surface while still being able to drift and absorb nutrients in the water. So, how do these seemingly delicate threads help mussels stay put?

From laboratory tests and computer models, scientists at the Massachusetts Institute of Technology (MIT) discovered that roughly 80 percent of the length of byssus threads — the same parts of the threads that connect the mussel to a hard surface on one end — is composed of stiff material, whereas the remaining 20 percent, at the end that is affixed to the mussel itself, is soft and stretchy. The combination of these different material properties likely helps the mussels adhere to surfaces, and enables them to survive the impact of various forces.

“It turns out that the … 20 percent of softer, more extensible material is critical for mussel adhesion,” Zhao Qin, a research scientist at MIT, said in a statement.

Researchers have studied byssus threads before, but Qin and his colleagues wanted to observe how these threads, and all their connecting parts, operate in simulated wave conditions.

“We figured there must be something else going on,” Markus Buehler, head of MIT’s department of civil and environmental engineering, said in a statement. “The adhesive is strong, but it’s not sufficient.”

The researchers placed an underwater cage in Boston Harbor for three weeks to see how mussels attached themselves to glass, ceramic, wood and clay surfaces. In the lab, the scientists used a tensile machine to test the strength of byssus threads as they were pulled and deformed.

Even though byssus threads have both stiff and stretchy properties, the filaments are made of a protein closely related to collagen, the researchers said. From their experiments, the scientists discovered that the distribution of stiffness along the threads is critical to their effectiveness.

Understanding how byssus threads work could help scientists design synthetic materials with similarly flexible properties, such as surgical stitches that connect tissues together. The findings could also help in the development of new building materials, sensors for underwater vehicles and other equipment that could be subjected to extreme conditions, the researchers said.