Chapter 8Marine Fish

Characteristics of Subphylum VertebrataA notochord that has developed into a spinal cord protected by

vertebrae and a head with a brain characterize organisms inthis subphylum. Vertebrates consist of the most complex, large, fast, and

conspicuous organisms. They include us, the organism that has had the most effect on the global biosphere.

Significance of Class AgnathaThis is the class of the jawless fish.

Species include lampreys and hagfish.Organisms in this class are significant because they may

represent the ancestor of bony fish/sharks. Scientists theorize that during the Cambrian period the first

of three gill arches on a jawless fish evolved into the first jaws. Having jaws allowed vertebrates to become very successful predators. Having jaws put organisms in class Chondrichthyes (sharks and rays) and

class Osteichthyes (bony fish) near the top of marine food webs.

Characteristics of Sharks and RaysClass Chondrichthyes includes sharks, rays and their

close relatives. Sharks and rays don’t look similar on the outside, but

share a basic anatomy that classifies them together. Sharks and rays are jawed fish, that lack a swim

bladder, and have cartilaginous skeletons.

Special Attributes of Sharks and RaysSharks and rays are successful predators:

Subclass Elasmobranchii have cartilaginous skeletons. This characteristic saves energy. Saving energy is one of the

things that have made them successful predators. Sharks have a sense of smell that detect incredibly

diluted substances. Sharks have a “conveyor belt” of multiple rows of teeth.

They swing into place as old teeth wear out and fall away.

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Special Attributes of Sharks and Rays (continued)

Sharks and rays have other interesting characteristics:Both have lateral lines – lines of sensory hair along the

length of the body that detect water motion and vibrations.

Unique to elasmobranchs is electroreception – the ability to sense minute electricity created by muscles and nerves.

Sharks and rays have organs called ampullae of Lorenzini which you can see as visible pits near their snouts used to detect the electrical current.

Special Attributes of Sharks and Rays (continued) Elasmobranchs differ in their reproductive strategy.

Sharks and rays produce fewer, but more mature offspring. Most fertilize their eggs internally.

The male deposits sperm in the female via a pair of copulatory organs called claspers found at the base of the pelvic fins.

The female lays an egg case in which the juveniles develop for up to six months at which time one or more sharks or rays emerge.

A few shark species are ovoviviparous – the eggs hatch within the mother’s body. They give birth to live young rather than egg cases.

The largest fish in the ocean. Shark size ranges from hand-sized to the

whale shark – the largest fish in the ocean. Whale sharks can reach 14 meters (46 feet). Basking sharks can reach 10 meters (33 feet). Megamouth sharks can reach 6 meters (20 feet).

All three are filter feeders that consume plankton.

Special Attributes of Rays Superorder Batidoidimorpha of subclass Elasmobranchii consists

of therays, which includes skates and guitarfish. Ray anatomy is well suited to life on sandy

bottoms or midwater. Specially adapted to life in midwater are

the eagle ray and manta ray. Pectoral fins have become “wings” that

stretch forward over the gills and are fused to the sides of the head.

Shoulder girdles are flattened and many bones are fused together for rigidity.

No longer need a tail for swimming, the tail has become a defensive whip in some species.

Rays literally fly through the water. The largest rays are mantas with wingspans

exceeding 8 meters (26 feet). Like the largest shark, the mantas feed on plankton.

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Characteristics of Bony FishClass Osteichthyes are jawed fish with bone skeletons.

Most have a swim bladder and scales. Most control buoyancy by adding or releasing gas

to/from their swim bladder. They control the swim bladders with oxygen gas exchanged to

and from blood circulation. Many have a special organ called the gas gland and the rete

mirabile that take up gases from the bloodstream for the swim bladder.

This allows many species to hover nearly motionless in midwater.

Most bony fish reproduce externally. The female lays her eggs, the male

immediately fertilizes them. Their strategy is to produce a vast number

of off-spring with only a few expected to survive to maturity.

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Characteristics of Bony Fish (continued)Bony fish have characteristics for life on the reef and for

life in theopen ocean: Bony fish have lateral lines that detect water

motion and vibrations. Most open ocean and schooling fish have a torpedo-like

streamlined shape that minimizes drag and turbulence. This fusiform shape is spindle-like, slightly broader at the

head and a V-shaped tail. This makes them fast swimmers.Most open-ocean and schooling fish have a lighter

underside and dark topside for concealment.Bony fish living in reefs and on the bottom use

survival strategies more diverse and includeconcealment and armor instead of swimming. For this reason, you see far more diversity in color,

shape, and size among reef and bottom fish.

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Types of Marine FishAgnatha

These jawless fish have a muscular, circular mouth with rows of teeth in rings

Long, cylindrical bodyLack paired fins and scales seen in other fishTwo types of jawless fish exist- hagfish and

lampreysEctothermic

Lamprey – www.wikipedia.com

Types of Marine FishHagfishes

– 20 species– Exclusively marine– They feed on dead and dying fish and marine

mammals primarily– Live in burrows in soft sediments– Produce large quantities of mucous from

glands in the skin to protect them while feeding

www.wikipedia.com

Pacific Hagfish (Eptatretus stoutii)

- 4 pairs of sensory tentacles around mouth- 12 pairs of gill slits- SLIME

Types of Marine FishLamprey30 speciesLive in freshwater (lakes) and salt waterAdults of some species spend a large portion of

their life in the sea, but return to freshwater to breed; adults normally die after breeding.

Parasitic: They feed on living fish by rasping into the sides of fish with their sucker-like mouth and consuming blood, tissue and body fluids Produce anticlotting agent

More Advanced Groups of FishFishes in the Classes Chondrichthyes and Osteichthyes are considered to be more advanced.

General Characteristics (advancements) seen in these groups:– Highly efficient gills– Scales cover the body – Paired fins – A wide variety of jaw and feeding types– Lateral line and other sensory organs– Streamlined body

Osteichthyes, The Bony FishSkeleton composed of boneMore species that all other vertebrates combined-

over 23,000 species worldwideGills used for respirationHinged jaws allow for a variety of different

feeding strategiesHomocercal tail (two lobes of equal size) provides

forward thrust

www.wikipedia.com

Osteichthyes, The Bony FishFlat bony scales protect body

ctenoid (tiny spines) or cycloid (smooth)Bony operculum covers the gills (provides

better protection against injury compared to gill slits for each gill)

Lateral line used in sensory capacity and communication

Swim bladder used for buoyancy control (some bottom dwelling fish lack swim bladder)

Variable body plans are adapted for specific environments

Osteichthyes, Body ShapeBody shapes vary greatly

dependent on the niche Ex. flounders and soles (flat

shape) live on the bottom and cover themselves slightly with sand to camouflage themselves from potential predators as well as prey

Osteichthyes – Body Shape of FAST fish

Tuna, billfish, and other fast moving predators are long, streamlined and most of their fins serve as rudders (very little flexibility except in caudal fin)

This body shape allows these predators to cut through the water quickly

Notice, too, that the area of the body called the caudal peduncle (area just before the tail) is very thin – this allows all the muscles to concentrate in this area allowing for greater thrust of the caudal (tail) fin (this means FAST swimming capabilities) Sailfish

Osteichthyes – Body Shape of not so fast fish

Angelfish – coral reef fish example – not open ocean fish

Angelfish and the like inhabit coral reefs, oyster reefs and other similar environments

In these fish, the body is not as streamlined and the fins are feather-like for lots of flexibility

This flexibility allows for greater control around the features that would be seen in a coral reef type environment (crevices, etc)– Humphead parrotfish

www.animalphoto.tk

Osteichthyes – Shape of fish that don’t swim far

Other fish have a shape that allows for camouflage in their environment

For example, fish like the toadfish and the stonefish actually look like rocks or “scenery” and thus can go undetected by predators or prey

www.fishimage.blogspot.comwww.njsciba.net

Osteichthyes – Color Patterns Countershading is seen in virtually all fish species In countershading, the ventral (belly) area of the

fish is lighter than the dorsal area of the fish This allows the fish to “blend in” with the

environment If a fish is seen from above, the darker coloration of

the dorsal area blends in with the darker color of the ocean bottom

If the fish is seen from below, the lighter coloration of the ventral surface blends in with the lighter coloration of the ocean surface

www.nationalgeographic.com

Osteichthyes, The Bony Fish– Coloration patterns:

Slower swimming fish often have bars or stripes that help break up the silhouette of a fish (a form of disruptive coloration)

This helps with predator avoidance Some also have coloration that helps them blend in

with environment (known as cryptic coloration)

www.sunysb.edu

Osteichthyes, The Bony FishColoration Patterns:Circular patterns on or near the caudal fin

Confuses predators who are not sure which end of the fish is the head

If fish attacked on caudal end where the black dot looks like an eye, she can probably get away with minor damage

If attacked on his head region, she may sustain serious, life threatening damage

Warning Coloration – use color to advertise their bad taste or poisonous

nature –

www.animalworld.comwww.fishwallpaper.net

www.inkart.net

Swimming PatternsFish exhibit an “s-shaped” swimming patternBands of muscle along the body called

myomeres drive this swimming motionDepending on the type of fish, different fins

may be used primarily for the forward movement

Swimming Patterns

A) eels swim by undulating body in lateral waves from head to tail

B) fast fishes with shorter bodies – flex caudal tailC) surgeonfishes, parrotfishes – move only the finsD) trunkfishes and porcupine fishes swim slowly

by moving base of tail and rest of body remains immobile

Specializations for swimming

Myomeres – bands of muscles that produce rhythmic contractions for swimming in S-pattern

Swim bladders in bony fish

Swimming PatternsIn bony fish, pectoral fins are not needed for lift (like in

sharks) and thus are normally not stiff in construction (exception: fast swimming species like tuna, billfish, etc)

In contrast, the pectoral fins in many bony fins are flexible and used for maneuverability

In some slower-swimming species, forward movement is mainly provided primarily by the pectoral fins (see fish in tanks! – coral reef fish)

In other species, all the fins may be flexible and highly modified for camouflage (example: sea horses and leafy sea dragons and weedy sea dragons

Fins will not allow for significant forward movement Flying fish example

Fish GillsThe construction of the gill is the same in

all fish – Gill arch supports the entire structure Gill rakers are on the forward surface of the gill

arch and Gill filaments trail behind the gill arch

Like in the human lung, exchange of oxygen and carbon dioxide takes place on these surfaces

Figure 8.17 The gills of fishes are very efficient for gas exchange. Bony fishes

have 4 pairs of gills (a), each containing 2 rows of gill

filaments (b). Lamellae in gill filaments (c) increase the

surface area of the gill filaments. (d) Diffusion of

oxygen from seawater into the blood gets a boost b/c the water flows across the lamallae in the opposite direction to that of the

blood. (e) The concentration of oxygen (indicated by

dots) is always higher in the water than in the blood. If

circulation were not reversed, blood to the body

would have less oxygen.

VIDEO

Acquiring and Processing FoodMouth structure also reveals the dietary preferences of fish

As an example, the “beak” (fused teeth) seen in parrotfish allows for these fish to scrape algae and other organisms off of hard surfaces

The butterfly fish uses its long tube-like mouth to feed on corals

While the barracuda uses rows of sharp teeth and a wide mouth to capture its prey – other fish

Acquiring and Processing Food Jaw/Mouth Structure

Acquiring and Processing Food:Mouth StructureThe position of the mouth is also importantA strongly forward facing mouth is important

in fish who chase down their prey (as seen in barracuda)

A downward facing mouth would be seen in fish feeding at/near the bottom (opposite for feeding on surface of water)

Acquiring and Processing Food:DigestionOrgans involved: stomach, intestine (with

anus), liver, pyloric caeca and pancreasThe stomach is structured very similarly to

the human stomach – stretch receptors in the wall of the stomach indicate when a meal is present and needs to be mechanically digested by the churning motion of the stomach wall

Acquiring and Processing Food:DigestionIntestine, pyloric caeca (tubes at end of

intestine), pancreas and liver (bile breaks down fat) all secrete digestive enzymes

The intestines of carnivorous fish tend to be short and straight while the intestines of herbivorous fish are longer and more coiled (plant and algae material is more difficult to process, so it needs to stay in the intestines longer)

Acquiring and Processing Food:Digestion

The Circulatory SystemTwo chambered heart that pumps blood

throughout the body (in contrast to the 4 chambered heart seen in mammals)

System of arteries, veins and capillaries takes blood to the body tissues and returns it for re-oxygenation by the gill filaments

O2 and CO2 diffuses across thin membranes of capillaries either in the gills or at the tissues of the body

Figure 8.15. The circulatory system of fishes consists of veins that carry deoxygenated blood (in blue) from the body, a two-chambered heart that pumps blood into the gills for oxygenation, and arteries that carry oxygenated blood (in red) to rest of body).

Fluid Balance in FishRemember osmosis and diffusion are

always at work in an organismFish need mechanisms to combat the

issue of water loss – OSMOREGULATIONFish osmoregulate by:

Swallowing seawater and expel the solutes in the digestive process (this allows them to keep the water and lose the solutes)

Most marine fish pass very little urine that is processed by the kidneys, and is highly concentrated with solutes with very little water content

Fig. 8.18 Marine fishes - salts excreted by

kidneys and drink water

The Fish Nervous SystemThe fish have a brain, spinal cord and numerous

nerves like other vertebratesSmell: Fish possess olfactory sacs (with

nostrils/nares)Hearing: Inner ears are set in fluid-filled canals

with sensory cells similar to the lateral line system.Taste: Detect chemical stimuli by using taste buds

are located in the mouth, lips, barbels and skinSight: The position of the lens changes like in a

camera (Note: Different from land animals where the lens changes shape for focusing on items

The Fish Nervous SystemAll fish rely heavily on the lateral line systemThe lateral line is a series of pores and canals

lined with specialized organs called neuromasts that are specialized to detect vibrationsLined with hair cells – similar to those in your

cochleaOrientation, predatory behavior, social

schooling

Fish BehaviorSchoolingWidely used (+4000 species school)Why school?

Predator deterrent Spawning aggrigation Migration Enhanced foraging

Fish BehaviorsTerritoriality

Some fish are territorial by nature all the time, others are only territorial during reproduction

Fish maintain their territories normally by “posturing” to show their aggression

Posturing can include raised fins, open mouth, darting, etc.

Fights between individuals are actually rareDamselfish and algae

Reproduction in FishSex hormones control the development of

sperm and eggs in fishRelease of sex hormones cued by water

temperature, day length, specific tide cycles, etc.

Broadcast spawning most commonSome fish have internal fertilization (sperm is

inserted directly into the female by the male)Complex mating behaviors are seen in some

species (Ex. Banggai cardinals, potato cod)Color or body changes can cue reproduction

Atlantic cod mating behaviors. 1. Male establishes territory. 2. Male makes displays (grunting,

spreading fins, etc). 3. Female (if the male is lucky) spawns with male.

Fish ReproductionSome fish are hermaphroditic

Simultaneous hermaphrodites – rare (ex. salmon, some deep sea fish)

Sequential hermaphrodites) Protandry - males then females (ex. anemone fish) Protogyny – females males (ex. wrasses, parrotfish)

Cues for changes - changes in social structure or environment

Fish ReproductionDepending on the species, fish can either be:

Viviparous – young are born liveOviparous - egg layers (most common)

Some parents protect eggs, though most do notOvoviviparous – eggs are kept inside and “hatch”

before being released from female reproductive tract

RARE: Parthenogenic species - in this reproductive plan, young develop directly from the unfertilized eggs of the female (no DNA from males) – the young are “clones” of the female