fisheries and aquaculture management lecture 5: fish and its environment

Fisheries and Aquaculture Management

Lecture 5:

Fish and its Environment

Class : PiscesFishes are poikilothermic (organisms with fluctuating internal temperatures), aquatic vertebrates with jaws.

The body is streamlined.

It is differentiated into head, trunk and tail. Between head and trunk, the neck is absent.

Locomotion is effected by paired and median fins.

Introduction

The body has a covering of scales.

They are of various types like placoid, cycloid, ctenoid and ganoid scales.

Placoid cycloid ctenoid

The body muscles are arranged into segments called myotomes.

The Alimentary canal consists of a definite stomach and pancreas and terminates into cloaca or anus.

Respiration is performed by gills. Gill slits are 5-7 pairs.

They may be naked or covered by an operculum.

The heart is two chambered (an auricle and a ventricle).

Basic Piscine Shapes

Most fishes fall into one of six broad categories based on body configuration: fusiform ( rover predator, piscivores (lie-in wait predator), surface oriented bodied fish, and eel-like fish.

The way a fish looks is a good indicator of how it "makes a living.“

Body shape, mouth location and size, tail shape and color can reveal a lot about a fish's lifestyle.

Fusiform:Fusiform, or streamlined, fish like the barracuda or jack are capable of swimming very fast. They usually live in open water.

This is the body shape that comes to mind when most people think of fish: streamlined (fusiform), with a pointed head ending in a terminal a narrow caudal peduncle tipped with a forked tail.

The fins are more or less evenly distributed about the body providing stability and maneuverability.

Such fish typically are constantly on the move, searching out prey, which they capture through pursuit.

Laterally compressed:Fish that are laterally compressed (flattened from side to side or flatfish) usually do not swim rapidly (some schooling fish are an exception).

However, they are exceptionally maneuverable.

Many, like the angelfish, are found near coral reefs.

Their shape allows them to move about in the cracks and crevices of the reef.

A flounder is a laterally compressed(deep-bodied) fish that live on its side on the bottom.

In these fish, the eye on the downward side migrates during development to the upward side, and the mouth often assumes a peculiar twist to enable bottom feeding.

Flat fish have the most extreme morphologies of bottom fish.

Depressed:Depressed fish (flattened from top to bottom), like stingrays, live on the bottom.

Bottom fish possess a wide variety of body shapes, all of them adapted for a life in nearly continuous contact with the bottom.

In most such fish, the swim bladder is reduced or absent, and most are flatten in one direction or another.

Bottom fish can be types: bottom rovers, bottom clingers, bottom hiders, flat fish and rattails.

Bottom rovers have a rover-predator-like body except that the head tends to be flattened, the back humped, and the pectoral fin enlarged.

Bottom clingers are usually small fish with flattened heads, large pectoral fins and structure (usually modified pelvic fins) that allow them to adhere to the bottom.

Depressed (Contd’):Such arrangements are handy in swift streams or intertidal areas that have strong current e.g. the gobies.

Bottom hiders are similar in many respects to the bottom clingers, but they lack the clinging devices and tend to have more elongated bodies and smaller heads.

These forms usually live under rock or in crevices, or lie quietly on the bottom in still water.

In contrast, skates and rays are flatten dorso-ventrally (depressiform) and mostly move about by flapping or undulating their extremely large pectoral fins.

Not only is the mouth completely ventral in these fish, but their main water intakes for respiration (the spiracles) is located on top of the head.

Eel-like:

They have elongated bodies, blunt or wedged shape, and tapering or rounded tails.

If paired are present they are small, while the dorsal and anal fins are typically quiet long.

Scales are small or embedded and even absent.

In cross section, their bodies can range from compressed to round.

Eel-like fish are particularly well adapted for entering small crevices and holes in reefs and rocky areas, for making their ways through beds of aquatic plants, and for burrowing into soft bottoms.

TailsThe shape of the tail can be an indicator of how fast a fish usually swims.

1.Crescent-shaped:Fish with crescent-shaped tails, like swordfish, are fast swimmers and constantly on the move.

2.Forked:Fish with forked tails, like the striped bass, are also fast swimmers, though they may not swim fast all of the time.The deeper the fork, the faster the fish can swim.

3.Rounded:Fish with a rounded or flattened tail are generally slow moving, but are capable of short, accurate bursts of speed.

Mouths

The location and size of the mouth can be a good indicator of the food a fish eat and where it lives.

Fish with large mouths generally eat large food items like another fish; however, the whale shark eats very small organisms which it strains from the water with its huge mouth.

Fish with small mouths eat small food items: small crustaceans or molluscs; and, fish with tiny mouths eat tiny things like zooplankton

Endotherms - animals who derive most or all of their body heat from their own metabolism e.g. Mammals, birds, some fish, and numerous insects are endothermic. A. Endothermic Regulation Advantages: The animal can remain active at a wide range of environmental temperatures. Note: The internal temperature of endotherms does have a range. It varies from time to time and place to place. However, the great constancy is the core temperature temperature deep within the body. The core temperature can vary such as in animals that hibernate. Disadvantages: 1) Endothermy takes a great deal of energy 2) Birds and mammals can't tolerate much change in their core temperature. 3) There are body size restrictions to endothermy - the animal can't be too small.

Ectotherms - animals who warm their body mainly by absorbing heat from their surroundings e.g. most Invertebrates, fish, amphibians, and reptiles.

B. Ectothermic Regulation Advantage: Takes little energy

Disadvantage: In cool weather, activities slow down Ectotherms can tolerate a wider range of temperatures than endotherms. Ectotherms generate their body temperature by behavior- absorbing sun or contact with a warmer surface.

Ecto- versus endothermic organismsBody temp of ectotherm (lizard) decreases with decreasing environmental temp, while the temp of the endotherm remains constant.The latter has to increase its metabolic rate (MR) in response to cold and hot. MR of ectotherm follows the change in environmental temp.Notice the much higher MR of endotherm.

Heat production and conservation in ectothermsHeat produced through muscle activity gets lost through the gill.Tuna, great white sharks and mackerels all have the ability to trap most of the heat through a countercurrent heat exchanger which maintains a constant gradient over a longer distance (incoming arteries are getting warmed up by outgoing veins) to transfer the heat.Why is this beneficial? Greater power output.

Heat production and conservation in ectotherms

Heat conservation: Countercurrent heat exchange Air conducts heat poorly and is therefore a good insulator.

Structures that trap air can insulate: the under-fur in mammals and down feathers in birds.

Decreased surface area: smaller appendages and larger body size. Decreased blood flow reduces heat loss. Water is an effective conductor of heat, quickly draining heat away

from an organism. Marine mammals either have fur or blubber.

How do endotherms maintain a constantly high temperature?

Thermoregulation in mammals and birds involves generating heat, retaining heat, and cooling mechanisms. 1.Thermiogenesis - active generation of heat through2.Oxidative metabolism 3.Shivering - rapid contraction of opposing muscle- The conversion of ATP to ADP releases heat.4.Non-shivering thermiogenesis - occurs in some mammals and a few birds; increase in metabolism triggered by hormones 5.Utilization of brown fat - fat with numerous mitochondria (thus brown color). These mitochondria release heat from metabolism and do not generate ATP. Brown fat is found in human infants, bats and hibernating mammals.


Brown adipose tissue: Abundant with fat and mitochondria, rich blood supply.

A protein called thermogenin uncouples the movement of protons across membranes from ATP production, burning fuel without producing ATP but heat is still released.

Found in newborn humans and many small mammals and hibernators.


2. Regulating heat exchange - slowing heat loss a) Vasoconstriction of vessels close to surface of body prevents heat

loss from blood flowing close to the surface. This also helps to keep core temperature stable. Costly- the limbs cool down and the muscles don't work as well.

b) Insulation - fat, boy hair, feathers

3. Regulating heat exchange - cooling a) Vasodilation of vessels close to surface of body allows heat escape

by radiation from blood vessels.b) Convection - heat lost by the movement of air across the surface of

the body; evaporative coolingc) Conduction - the direct transfer of heat by contact to a cooler solid;

such as an animal sitting in a pool of cold water or on a cool rock.Endotherms also can help to regulate their temperature by behavioral

mechanisms: ceasing activity and finding a cooler environment.


Controlling thermoregulation In humans, the hypothalamus, the body's thermostat, monitors the temperture of the blood flowing through it and also receives information from sensory receptors in the skin.

In response to temperatures below the normal range, the thermostat activates thermiogenesis and heat-saving mechanisms.

In response to warmer temperatures, the thermostat activates body cooling mechanisms such as vasodilation, sweating, or panting.

Recall: The pressure at depth d in a liquid is

where ρ is the liquid’s density, and p0 is the pressure at the surface of the liquid. Because the fluid is at rest, the pressure is called the hydrostatic pressure. The fact that g appears in the equation reminds us that there is a gravitational contribution to the pressure.

Q. What Causes Buoyancy? : Pressure!

Hydrostatic Pressure

A floating object is in static equilibrium

Buoyancy

Fishes have two means of maintaining buoyancy Neutral buoyance Regulation by swimbladder

Neutral Buoyancy Many fish are functionally weightless in water This allows them to save energy while staying in a

certain area

Q. What is Required for Neutral Buoyancy?Specific gravity must equal that of surroundings

Fresh water sp. gr. = 1 Salt water sp. gr. = 1.026

Different regions may have slight specific gravity differences due to dissolved materials

Strategies to Maintain Neutral Buoyancy

1.Body made of large quantities of low density compounds

Low Density Bodies Many fish have large quantities of lipids

Specific gravity < 1 Large livers filled with squalene

Hydrocarbon sp.gr. 0.81. A few fish have trigliceride oils in bones


2.Fins are shaped and angled to generate forward lift

Fins Designed for Lift Leading edges of fins help maintain

position Small amount of energy gives large

amount of lift Also, body drag is eliminated by shape of

fins and body


3.Reduction of heavy tissues like bone Bones are thin

Living in water does not require as much support

Sp. gr. of bone = 2.0 Cartilage is less dense than bone

Sp. gr. = 1.1 Many fish do not have a bony skeleton


3.Having a swimbladder filled with an appropriate amount of air

Major organ for buoyancy control Allow for precise control of total body

specific gravity Normally 5% of marine fish body, 7% of

freshwater body

Types of Swimbladders

1.Physostomous Swimbladders Fish must swallow air to deliver it to the

swimbladder Requires these fish to live in shallow water They cannot take in enough air to be buoyant at

deep water and actually move to deep water

2.Physoclistous Swimbladder Swimbladder is inflated via circulatory system

1. Rete mirabile (wonderful net) 2. Gas gland

Fish are able to live away from the surface

Regulation by Swimbladders

1.Modified Swimbladders Some fish have more than one swim bladder

Often fish with great vertical movements Allows them to gain or lose air more quickly

2.Bottom Dwellers Swimbladder is not needed

ReducedAbsent

The normally bottom dwelling sea robin can use their pectoral fins to produce lift while swimming.

http://en.wikipedia.org/wiki/Sea_robin

Regulation by Swimbladders3.Species Living in Flowing Water Usually have reduced swim bladders Less buoyancy helps them to maintain a given area Their buoyancy requirement is met by other means than the swimbladder

4.Mola mola Has no swimbladder Commonly a surface dweller – sometimes floats on the surface Large amounts of body fluid that are about ½ the specific gravity of seawaterThe cartilaginous fish (e.g. sharks and rays) and lobed finned fish do not have swim bladders. They can control their depth only by swimming (using dynamic lift)

Uptake of oxygen in and carbon dioxide release from the fish During respiration fish, like other animals, take in oxygen

and give out carbon dioxide.

The process is done by using gills in almost all fish although some can also use the skin and some have lung like structures used in addition to gills.

When a fish respires, a pressurised gulp of water flows from the mouth into a gill chamber on each side of the head.

Gills themselves, located in gill clefts within the gill chambers, consist of fleshy, sheet like filaments transected by extensions called lamellae.

Uptake of oxygen in and carbon dioxide release from the fish

Diagram showing the structure for respiration (gas exchange) in fish.

Uptake of oxygen in and carbon dioxide release from the fish As water flows across the gills, the oxygen within them

diffuses into blood circulating through vessels in the filaments and lamellae.

Simultaneously, carbon dioxide in the fish’s bloodstream diffuses into the water and is carried out of the body

Effects of oxygen levels on oxygen uptake by fish It is commonly thought that if there is not enough oxygen

in the water, then the fish will be seen gasping at the surface but this is a last resort means to breathe.

The first indication there may be a dissolved oxygen problem in the water is when the fish become unusually lethargic and stop feeding.

As oxygen levels decrease, the fish do not have enough energy to swim and feeding utilizes yet more oxygen.

In terms of managing any aquatic system, it is always advisable to increase the aeration when any fish start to behave abnormally, before adding any form of medication to the water.

Osmoregulation and Excretion

An organism maintains a physiological favorable environment by osmoregulation, regulating solute balance and the gain and loss of water and excretion, the removal of nitrogen-containing waste products of metabolism.

Osmoregulation balances the uptake and loss of water and solutes.

Over time, the rates of water uptake and loss must balance.

Osmoregulation and ExcretionWater enters and leaves cells by osmosis, the movement of water across a selectively permeable membrane.Osmosis occurs whenever two solutions separated by a membrane differ in osmotic pressure, or osmolarity (moles of solute per liter of solution).If two solutions separated by a selectively permeable membrane have the same osmolarity, they are said to be isoosmotic.There is no net movement of water by osmosis between isoosmotic solutions, although water molecules do cross at equal rates in both directions.When two solutions differ in osmolarity, the one with the greater concentration of solutes is referred to as hyperosmotic, and the more dilute solution is hypoosmotic.Water flows by osmosis from a hypoosmotic solution to a hyperosmotic one.

Osmoregulators expend energy to control their internal osmolarity; osmoconformers are isoosmotic with their surroundings.An osmoregulator is an animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment.An osmoregulator must discharge excess water if it lives in a hypoosmotic environment or take in water to offset osmotic loss if it inhabits a hyperosmotic environment.Osmoregulation enables animals to live in environments that are uninhabitable to osmoconformers, such as freshwater and terrestrial habitats.It also enables many marine animals to maintain internal osmolarities different from that of seawater.Whenever animals maintain an osmolarity difference between the body and the external environment, osmoregulation has an energy cost.

Osmoregulation and Excretion

Most animals, whether osmoconformers or osmoregulators, cannot tolerate substantial changes in external osmolarity and are said to be stenohaline.

In contrast, euryhaline animals—which include both some osmoregulators and osmoconformers—can survive large fluctuations in external osmolarity.

For example, various species of salmon migrate back and forth between freshwater and marine environments.

The food fish, tilapia, is an extreme example, capable of adjusting to any salt concentration between freshwater and 2,000 mosm/L, twice that of seawater.

Osmoregulation and ExcretionMarine vertebrates and some marine invertebrates are osmoregulators.

For most of these animals, the ocean is a strongly dehydrating environment because it is much saltier than internal fluids, and water is lost from their bodies by osmosis.

Marine bony fishes, such as cod, are hypoosmotic to seawater and constantly lose water by osmosis and gain salt by diffusion and from the food they eat.

The fishes balance water loss by drinking seawater and actively transporting chloride ions out through their skin and gills.

Sodium ions follow passively.

They produce very little urine.

Osmoregulation and ExcretionMarine sharks and most other cartilaginous fishes (chondrichthyans) use a different osmoregulatory “strategy.”

Like bony fishes, salts diffuse into the body from seawater, and these salts are removed by the kidneys, a special organ called the rectal gland, or in feaces.

Unlike bony fishes, marine sharks do not experience a continuous osmotic loss because high concentrations of urea and trimethylamine oxide (TMAO) in body fluids leads to an osmolarity slightly higher than seawater.

TMAO protects proteins from damage by urea.

Consequently, water slowly enters the shark’s body by osmosis and in food, and is removed in urine.

Osmoregulation and ExcretionIn contrast to marine organisms, freshwater animals are constantly gaining water by osmosis and losing salts by diffusion.

This happens because the osmolarity of their internal fluids is much higher than that of their surroundings.

However, the body fluids of most freshwater animals have lower solute concentrations than those of marine animals, an adaptation to their low-salinity freshwater habitat.

Many freshwater animals, including fish such as perch, maintain water balance by excreting large amounts of very dilute urine, and regaining lost salts in food and by active uptake of salts from their surroundings.

Osmoregulation and ExcretionSalmon and other euryhaline fishes that migrate between seawater and freshwater undergo dramatic and rapid changes in osmoregulatory status.

While in the ocean, salmon osmoregulate as other marine fishes do, by drinking seawater and excreting excess salt from the gills.

When they migrate to fresh water, salmon cease drinking, begin to produce lots of dilute urine, and their gills start taking up salt from the dilute environment—the same as fishes that spend their entire lives in fresh water.

Excretion of Wastes Elimination of nitrogenous waste products from the body is a

process called excretion. The excretory products are formed during the amino acid

catabolism. These excretory products are-harmful to the body, if they are

accumulated. In some animals that live partly in water and partly on land, in such

forms the toxic ammonia is changed into less toxic urea in liver. Urea can be retained in the body for much longer period than

ammonia. Terrestrial animals which have scarcity of water cannot afford to

loose water from their body; In such forms nitrogenous waste is converted into still less toxic substance called uric acid. It is excreted in crystalline form.

Excretion of Wastes Animals that excrete nitrogenous wastes as ammonia

need access to lots of water.

This is because ammonia is very soluble but can be tolerated only at very low concentrations.

Therefore, ammonia excretion is most common in aquatic species.

Many invertebrates release ammonia across the whole body surface.

In fishes, most of the ammonia is lost as ammonium ions (NH4

+) at the gill epithelium.

Freshwater fishes are able to exchange NH4+ for Na+ from

the environment, which helps maintain Na+ concentrations in body fluids.

Excretion of Wastes Because ammonia is so toxic, it can be transported and

excreted only in large volumes of very dilute solutions.

Instead, mammals, most adult amphibians, sharks, and some marine bony fishes and turtles excrete mainly urea.

Urea is synthesized in the liver by combining ammonia with carbon dioxide and is excreted by the kidneys.

The main advantage of urea is its low toxicity, about 100,000 times less than that of ammonia.

Urea can be transported and stored safely at high concentrations.

This reduces the amount of water needed for nitrogen excretion when releasing a concentrated solution of urea rather than a dilute solution of ammonia.

Excretion of Wastes The main disadvantage of urea is that animals must

expend energy to produce it from ammonia.

The amount of nitrogenous waste produced is coupled to the energy budget and depends on how much and what kind of food an animal eats.

Because they use energy at high rates, endotherms eat more food—and thus produce more nitrogenous wastes—per unit volume than ectotherms.

Carnivores (which derive much of their energy from dietary proteins) excrete more nitrogen than animals that obtain most of their energy from lipids or carbohydrates.

Excretion in fishes

The functions of excretion and osmoregulation are closely related and are performed by gills and kidneys in fishes.

Excretion and Osmoregulation in Freshwater FishesBecause of hyperosmotic body fluid they are subjected to swelling by movement of water into their body owing to osmotic gradient.

Since the surrounding medium has low salt concentration, they are faced with disappearance of their body salts by continual loss to the environment.

Thus, freshwater fishes must prevent net gain of water and net loss of salts.

Net intake of water is prevented by kidney as it produces a dilute, more copious (i.e. plantiful hence dilute) urine

Osmoregulatory inflow and outflow of salts and water in a fresh water fish. HpU, hypotonic urine, S, salt , W, water, W+S, water and salt

Excretion and Osmoregulation in Freshwater Fishes

Excretion and Osmoregulation in Freshwater Fishes

The useful salts are largely retained by reabsorption into the blood in the tubules of kidney and a dilute urine is excreted.

Although some salts are also removed along with urine which creates torrential loss of some biologically important salts such as KCI, Nacl, CaCI2 and MgCI2, which are replaced in various parts.

Freshwater fishes have remarkable capacity to excrete Na+ and Cl- through their gills from surrounding water having less than 1 mm/L NaCl, even though the plasma concentration of the salt exceeds 100 mm/L NaCl.

Thus NaCl actively transported in the gills against a concentration gradient in excess of 100 times.

In these fishes the salt loss and water uptake are reduced by the integument considerable with low permeability or impermeability to both water and salt also by not drinking the water.

Excretion and Osmoregulation in Fish

Exchange of water and salt in some fishes.(a)Marine elasmobranch does not drink water and has isotonic urine.(b)Marine teleost drinks water and has isotonic urine.(c )Fresh water teleost drinks no water and has strongly hypotonic urine.ASG, absorbs salt with gill; Hr NaCI(RG), hypotonic NaCI from rectal gland; SS (G), secretes salts from gill; W, water.

Excretion of Wastes in Marine Water Fishes

Modern bony fishes (marine teleosts) have the body fluid hypotonic to seawater, so they have tendency to lose water to the surroundings particularly from gill via epithelium. The lost volume of water is replaced by drinking salt water.

About 70-80% sea water containing NaCl and KCl enters the blood stream by absorption across the intestinal epithelium. However, most of the divalent cations like Ca++, MG ++ and SO 4 which are left in the gut are finally excreted out.

Excess salts absorbed along with sea water is ultimately removed from the blood with the help of gills by the active transport of Na+, Cl sometimes K+ and eliminated into the seawater.

However, divalent ions are secreted into the kidney.

Excretion of Wastes in Marine Water Fishes Thus urine is isosmotic to the blood but rich in those salts,

particullarly Mg++, Ca ++ and SO4 which are not secreted by the gills. Combined osmotic action of gills and kidney in marine teleosts

resulted in the net retention of water that is hypotonic both to the ingested water and urine.

Osmotic regulation in marine boney fishes. HpU, hypotonic urine: SW, sea water, W+S+NH3 , water, salt and ammonia, W. water

fisheries and aquaculture management lecture 5: fish and its environment

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