See glossary at completion of presentation.

The growth of fishes is an important indicator of environmental and physiological conditions. The growth of fishes is extremely flexible because it is often the last process in the balanced energy equation that is performed by fish. Simply stated, metabolism, osmoregulation and activity must all be accomplished first, and whatever energy is left will become available for growth. Small differences of energy expenditure in these result in large differences in growth. Since growth is so strongly related to the environment through temperature and food availability, it differs in every ecosystem.

Although some may not find the study of the metabolism of fishes of much excitement, a short review of the process is needed because it is a major determinant of growth. Energy accumulated for growth is the difference between the quantity of food eaten and the amount required for catabolism. Carp, like all fish in a body of water function as closed systems and follow the laws of thermodynamics which means all energy ingested must be accounted for in energy use or growth. Survival of an individual fish does not require breeding or growing. Species survival however requires successful reproduction. It is significant to know that the yearly spawn is perhaps the most costly activity concerning the growth of spawning age fish. Many fish will not recover sufficiently to begin growing until the onset of summer in temperate climates. More is to be said later on this subject of size and spawning, but first our review of metabolism and the energy equation.

pQr+Qm+Qg

Q simply represents an energy change. Qr represents the ration or amount eaten. Qm for metabolism affected by temperature and activity, and Qg for growth.

The value of p includes assimilation efficiency or the energy absorbed from food eaten. Not all the energy ingested can be assimilated. Assimilation efficiency indicates how well ingested material can be broken down to nutrients like glucose, free fatty acids and triglycerides. If a carp eats a diet high in plant material, especially cellulose, this is not very digestible and most of the energy is lost as feces. If the same animal eats plant material rich in digestible sugars (e.g. wild berries) much of the food is digestible and little ends up as feces. A diet of crayfish (with much indigestible chitin) or earthworms will affect the value of p. Once assimilated, then available energy can be used in body maintenance or growth. The use of energy for normal body functions is termed catabolism. The term anabolism is the storage of energy for growth, energy reserves, or reproduction. This is one of the simplest forms of energy budgets. I have avoided detailed energy budgets which itemize even the cost of the elimination of feces, and ammonia excretion via the gills. The important issue is that we can see a relation to growth and realize growth is sacrificed for metabolic needs and reproduction. Our end goal will be to put this all together to understand why some waters will hold and support big fish and others will not. Remember fish in different waters have different equations unless the resources and environmental conditions are the same. The biomass in the Great Lakes differs drastically from the biomass of a river system. The seasonal temperatures of the Northeastern US will differ from the Southeast US and where do you think the largest carp will be found?

Metabolic Considerations of fish growth.

Most fishes are ectothermic poikilotherms, whose body temperatures change in accord with ambient water temperatures. Metabolic rate and chemical processes will relate to water temperatures. As body temperature changes, temperature influences the rate of enzyme activity, mobility of gases, diffusion and osmosis. Standard metabolism is related to metabolic rate and temperature. Biological processes are enzymatically controlled and have optimal temperatures at which they operate. Certain enzymes produce substrates more rapidly at a lower temperature than at a higher one. Acclimation is the process carp use to acclimate physiologically to higher or lower than optimal temperatures to produce enzymes with different thermal capabilities. Biologists also include an active metabolism to include the range of activity a fish performs to go about it's life processes (e.g. swimming against a river current or eluding predators, or active procurement of forage.) A fish must maintain at least a standard metabolic rate to survive, and cannot exceed an active metabolic rate, at least not on a sustained basis. The difference between these two metabolisms is termed the scope of activity. All the life processes such as digestion, osmoregulation and locomotion must remain between these two metabolic levels. Maximum scope (highest efficiency) does not occur at the coldest temperature, or at the warmest temperature, but rather at an intermediate temperature.

Biologists have calculated the maximum scope for carp at a temperature near 20 C (68 F). At this temperature, a fish can have the largest variation of metabolic activity, where it might be able to swim the fastest for example. Higher temperatures become more stressful. As temperatures increase, the ability of water to hold oxygen declines, yet the metabolic rates of the fish increases. This is the double penalty of temperature increase.

It is known that carp have the advantage to adapt to a wide range of temperatures which would be fatal to other species of fish which can only exist in a narrow band of temperature. Trout can acclimate to warmer temperatures to a small degree. Tropical fishes are likewise restricted to warmer climes. Carp which had acclimated to cold temperature (10 C) had higher metabolic rates and maintained higher levels of metabolism than carp which had acclimated to (20 C), and were tested at 10 C. Just the opposite occurs at warmer temperatures. At excessively warm temperatures the metabolic rate would become even higher which would waste energy. Acclimation at high temperatures reduces metabolic rate to conservative levels again. The point to remember is that high metabolic rates waste energy needed for homeostasis, reproduction and lastly growth. There are many waters which produce many eight to twelve pound fish but lack the production of larger fish. A look at the balanced energy equation can help understand why. If forage quality is present and ration per population is adequate, temperature may be limiting the attainable growth because higher than optimal temperatures are above that which the fish can acclimate to. Adult fish in this water will spawn if they have the energy reserves and that will cause a distinct growth check which will be evident on the scales of the fish. Remember growth is the last utilization of energy and higher metabolism wastes it.

The carp is a cold water, temperate fish. Fish in temperate climates are robust in their temperature capabilities. They live near 0 C every winter and as high as 30 C every summer. They have evolved considerably to maintain high metabolic rates at cold temperatures which is what an individual fish does during acclimation. A reophilic wild population in the Danube is assumed to be the origin of the European species and is presently under threat. A recent radio telemetry study indicate that carp are among the most active during cold temperature periods and covered twice the range of brown trout or suckers. The body style of trout and carp are alike in that they are fusiform. The fusiform shape is also known as the predator/ rover. Trout have small scales typical of fish which do not roam widely in their ranges and are predatory. Fish with larger scales such as the carp will follow the roving pattern and has evolved the larger scales as an armor against predators. This level of higher activity of carp during winter indicates that carp have an energy requirement and will feed in this cold water period. It is an indication that carp are able to feed, grow, and conserve energy which will be available for the demands of the spawn when that time arrives in the spring. Carp found in warmer climates do not have the benefit of colder temperatures needed to develop these energy reserves and are forced to live life in the 'fast lane', and subsequently age at a faster rate. Higher temperatures throughout the year impose a penalty on growth and longevity.

Digestion and Nutrition, and other energy uses

Feeding experiments show an elevation in metabolic rate over a period of time after a fish has eaten. In short there is a cost to the ingestion, digestion and excretory functions of whatever a fish eats which need to be overcome before growth can occur. In other words a fish must be able to assimilate and utilize whatever is presented to it. Nutritional deficiencies do exist in the natural and commercial pond settings which must include stocked waters where fish need a supplemented diet. Included in this category are the stocked waters when the carps diet is supplemented only by baits presented by anglers.

Carp are omnivorous and have longer hind guts than fish which are primarily carnivorous. They lack a highly developed stomach and do not require low pH gastric acidity to digest whole fish as a piscivore would. Maceration of larger or harder forage is accomplished by pharyngeal dentition which is dorsally located at the entrance to the esophagus. This aids assimilation greatly. The pharyngeals are also thought to strain excess water from the bolus of forage prior to passage into the esophagus.

Gill rakers are highly developed in the carp. Form follows function in anatomy. In piscivorous fishes e.g. largemouth bass, the gill rakers are short, stout and widely spaced. They function in preventing prey from escaping through (and damaging) the gills. The carp possess intermediate gill rakers which are closely spaced. Marine rovers e.g. menhaden usually have the longest and most tightly spaced gill rakers and are primarily planktonic feeders. However the carp among freshwater species are among the most developed in number and closeness of spacing. The diet composition of carp indicate they are specialists in plankton feeding and filter the smallest of forage for subsistence. Forage the size of grains of rice or even the smallest of wind blown seeds are the staple forage of the largest of carp. In certain waters known for populations of large sized carp such as the Great Lakes, the largest of fish are often found on the surface feeding on insects in water fifty or sixty feet deep, far too deep to host the populations of crustacea found along the littoral zone near shore. It is a widely believed myth primarily among anglers that large carp require larger forage as they reach full growth (asymptote). That idea is changing as the largest of specimens are being caught by fly and grub fisherman seeking the largest fish well away from the shoreline. Carp in excess of forty pounds have been observed preoccupied by insects on the surface. In some waters detritus was the primary food source. In others zoobenthos comprised the highest percentage. In an ecosystem such as the Great Lakes, carp populations able to forage on the mountains of zooplankton and fish larva replete with yolk sacs, would out grow carp which foraged primarily on detritus. The bio mass amounts to metric tons of plankton and baitfish in these waters. Bait falls are common and occurs frequently and the benthic animals are recipient of them. Carp are considered demersal in their feeding which means they feed on the bottom, but they are found feeding at all levels opportunistically. A form of zooplankton commonly found at this point in time would have been rare two weeks ago, and will have a short cycle followed by one of another species. It is important to note that zooplankton are not invisible and microscopic animals but can be rather large. Jelly fish are an example of plankton and many varieties are too large for carp to engulf. Many species of fish deposit their eggs among clouds of zooplankton. Plankton refers to any animal which is a poor swimmer and drifts along in the current. Many varieties of plankton develop a vesicle of oil to maintain buoyancy and is almost nutritionally perfect as a single source of forage. Zooplankton feed on phytoplankton which are minute free floating plants e.g. algae.

Carbohydrates derived from plant sources are of lessor importance to carp and the more complex carbohydrates are difficult to digest and assimilate. Simple sugars will yield fuel for immediate use. Proteins are among the most costly to utilize for food and are used primarily for anabolic growth. Fats and triglycerides are the most effective fuel and is storable for energy reserves. Carp store lipids in the liver for reserve use. Protein cannot be broken down efficiently enough or very quickly for use as a reserve fuel. The body composition of carp is considered lean in comparison to fish such as salmon which store their energy reserves throughout the muscle tissue. All vitamins are important and essential amino acids must be derived from the diet.

Carp which are omnivores consume nearly five and a half times their body weight in forage per year around the mean temperature of 20 C. (68 F) If the food is of poor value the amount will be higher. Experiments done on gold carp indicate that they become satisfied with a certain ration of food given to them. With temperature remaining constant, the gold carp were permitted to eat all they wanted, ad libitum. Eventually they arrived at a level of satiation and a consistent amount was measured. Experimenters then cut the rations with kaolin which added the same bulk but contributed nothing nutritionally. The gold carp began to consume more of the ration allowed to compensate for the decrease in nutritional value. This simple experiment indicates that fish may have control of their growth through food selection. Other studies done on carp indicated that when fed unlimited amounts of ration, carp ate to the point of distress. In other words they over consumed which was detrimental and affected the balanced energy equation adversely. Carp were the only fish studied that produced these results. Carp fed strictly high protein baits developed grossly distended abdomens and did poorly on respirometry testing. It is unlikely that in nature fish eat satiation diets; instead they consume limited rations on a day to day basis. Field studies indicate deficiencies exist and each water is different. A study on young fish living close to shore ate a diet of detritus with a composition of 14% protein. Adult fish remained in deep water and ate detritus found there with only a 2% protein content. The adult fish preferred to remain in deeper water and were deficient in their diets as compared to the younger fish.

The younger fish which were still growing required the advantage in nutrition which the fully grown carp did not. Fully grown carp had less of a requirement as they needed only enough nutrition to maintain homeostasis. Fully grown carp are loathe to leave the environs of deeper water. The younger, still growing carp seem to have little choice but to frequent the littoral zones because of the biodiversity available for forage. In aquatic animals carbohydrates are not important energy sources, they are not a large component of the diet, and they are a very small component of any energy stored in the body itself. For fish, metabolizable energy for lipids decreases to about 8.0 kcal/g, of protein to 4.23, and of carbohydrates to 1.6. An average carbohydrate is only about 40% digestible, while a lipid is about 85% digestible. Keeping this in mind, let us look at the growth of the carp.

Growth

The most common means to evaluate growth is to examine the length of individual fish over time. Fish collected regularly from a lake show regular changes in length as they grow older, resulting in an asymptotic curve. Fishes reach asymptotic (maximum) lengths later in life, and if they lived after reaching these lengths, growth would cease. Equations have been developed to determine growth and maximum size. These equations demonstrate that as fish grow larger, smaller fish grow larger faster in length than larger fish of the same species. Carp immediately after hatch grow exponentially and rapidly outgrow most other species as well. They spawn early as well in the spring. All this adds to the survivability of the species. Ecologists are generally more interested in growth in mass, rather than length. Because calories and energy and temperature changes cannot be easily expressed in length, the balanced energy equation is again applicable to growth expressed in mass.

The simplest method is to weigh a live fish which will yield its wet weight. Weigh the fish immediately upon capture because the fish may weigh less later due to excretory loss of water and feces caused by stress. On the other hand, fish may also absorb water under duress. An inverse relationship exists between lipid and water content. Lipid levels used for winter activity and gonad maturation are depleted until after the spawn. During this time water weight increased in these fish. When forage is abundant, lipid levels are repleted and body water content changes seasonally. For this reason more accurate measurements are utilized such as removal of water in an oven and performing dry weight experimentation. Direct calorimetry is then performed on the dry contents.

Variables affecting growth are ration, maintenance, endogenous control of growth, acclimation temperature, temperature cycles, and other environmental factors. The most important is ration. If an animal does not eat it loses weight. Zero ration results in negative growth. A fish requires some level of ration to reach zero growth. There is also an internal limit to ingestion, and as ration increases from zero to that limit, growth increases at a declining rate until it eventually reaches asymptote. The first of two most basic levels of ration are maintenance which is the amount required to maintain body weight. This compares to standard metabolism in ration terms. Energy use at standard metabolism is actually less than at maintenance ration, because at maintenance ration a fish may swim and has heat increment costs, nitrogen excretion and assimilation deficiencies. Those processes increase metabolism above standard. The second is satiation or maximum ration a fish can eat. Usually maximum ration results in maximum growth. Carp exhibit a glutton effect in that at maximum ration these fish cannot digest as efficiently, and growth declines.

Constant temperature and growth

For poikilothermic animals, temperature influences a variety of processes that affect growth. Maintenance ration increases continually with temperature, while maximum ration reaches an optimum at intermediate temperature and then declines. Since the difference between these two rations is related to growth, growth is maximum at an intermediate temperature 20 C (68 F) The optimum temperature for growth is generally lower than the optimal temperature for consumption because of the increasing costs of maintenance at higher temperatures. At reduced ration, optimum temperature for growth is lower than at maximum ration. A fish may move into cooler water to adjust to limited ration. That would result in a lower maintenance requirement, and therefor, better growth on that fixed ration. Fish might trade off among the best temperatures for metabolism, consumption or growth by moving into different temperature locations in a lake or stream.

Vertical migration

In 1971 researchers predicted that they would find sockeye salmon stratified at their optimal temperatures in the field. They predicted that sockeye salmon in nature should occur at 12 C (optimum for growth) if food was unlimited, or at slightly cooler temperatures if food were limited. The actual pattern of their predictions were found to be neither, but rather showed vertical migration. Sockeye salmon moved up in the water column and fed in warm surface water in early morning and late at night, and then moved deeper during the middle of the day into hypolimnetic waters. At 12 C, which might be their preferred temperature , they found little food; they could remain there and be perfectly comfortable, but not have much to eat. However if the fish moved to warmer surface water to feed, their growth was limited by temperature. The resultant strategy was to move into even cooler water when they were not feeding, which appeared to reduce metabolic rate and increase growth. Since then, many researchers have established the pattern of vertical migration. Vertical migration is not only common in fishes but also in zooplankton populations. This is a common phenomenon in lakes and oceans. Researchers have hypothesized that one explanation for this migration might be that zooplankton avoid visual predators by moving to the surface at dark. The zooplankton themselves may do this to optimize growth as animals metabolize less at cooler temperatures and therefor grow better under fluctuating temperatures.

Carp are commonly seen on sonographs occupying the water column near or below the thermocline (metalimnion). Temperature readings will most likely be near the optimum temperature, or lower, for these suspended fish. Lakes which are found in the Northern hemisphere and are deep enough to stratify in this manner are the most likely to harbor very large carp. Riverine systems will also hold temperature variations where cold water effluent from springs are found. River systems which are controlled by dams e.g. the St. Lawrence, will also emulate lake systems and allow fish to suspend in optimal temperature ranges. The massive lake formed by the Roosevelt and Iroquois dams on the St. Lawrence river known as the Lake of St. Lawrence hosts bait fish and plankton populations and is known for populations of large carp. Generally the current movement of river systems (lotic) do not stratify vertically as lakes (lemnic) do.

Each fish in a system has an individual capacity to attain a certain size. Each fish is limited by genetics and carp populations around the world are comprised of different races with wide variations of growth potential. Some researchers number five separate races. All are cyprinius carpo of the family cyprinidae. Carp growth is well studied. The carp enjoys sport fish status in the European countries and is a major food source in many countries. It has world wide commercial impact and is one of the most farmed fish commercially. Millions of tons were farmed annually for consumption in the US in years past although production today has fallen off with decreased demand.

Most researchers believe carp reach asymptote after fifteen years of possible growth. This is when skeletal potential for growth ceases. It is a time when further growth of the annular rings of the scales end. After this time receding of the scale indicating retardation of growth is seen in some cases of negative growth, disease or stress. Growth continues under favorable conditions and increases in girth and body mass are noted. It would seem to hold true that carp which attain maximal length have the greatest potential. Terminal growth of carp may be five to fifty pounds depending on the individual fish, race, environment, etc. In sexually mature fish that participate in the spawn, reading of the annular rings of the scale indicate a deep check which represents a retardation of growth. The spawn requires a tremendous amount of energy resources for gonadal development and energy expenditure during the spawning period. Certain individual carp do not spawn each season and make spectacular growth progress. Older fish, usually above thirty pounds among the Galician strain in the northern hemisphere, begin to attain great mass under the most ideal conditions and go on to become specimen fish. What is the longevity of an individual carp. Researchers estimate nearly twenty-six years while allowing for an excess of the norm. The general evidence is that the longer an animal takes to reach maturity, the longer the life span and individual waters produce different results.

Keep the balanced energy equation in mind. Within in it are the many variables that affect growth. The equation raises a myriad number of questions which need to be answered for each location of water where carp are found.

Glossary

asymptote- in mathematics represents a limit to a curve used on a graph but refers to maximum growth attained by a fish, according to a growth formula plotted on a graph.

demersal- dwelling at or near the bottom of a body of water.

detritus- debris, disintegrated or eroded organic matter used a a food source by fish and other aquatic animals.

ectothermic- pertaining to an organism which regulates its body temperature by exchanging heat with its surroundings.

hypolimnion- the layer of water in a thermally stratified lake which lies below the thermocline, is non-circulating and remains perpetually cold.

littoral zone-the zone of or near the shoreline of a body of water.

metabolism- physical and chemical processes occurring within the cell of a living organism necessary for the maintenance of life. Some substances are broken down releasing energy as in catabolism, and others are synthesized or stored as in anabolism.

osmoregulation- maintenance of an optimal, constant osmotic pressure in the body of a living organism.

piscivore-an animal that subsists on fish. A fish that subsists on other fish.

poikilotherms- see ectotherms

riparian- relating to the banks of a body of water.

reophilic- preferring to live in flowing water.

Resources

Biology and Ecology of Fishes

James S. Diana

Fishes, An introductory to Ichthyology

Peter Moyle, Joseph Cech, Jr.

The Infinite River, A biologists vision

William H. Amos

Carp and the Carp Angler

George Sharman

FishBase

Species summary for cyprinius carpo

Field research and video support

Carp research team:

Alan Kowaleski

Michael Malone

Andy Boyle  United Kingdom