Ichthyology Exam 1

Requirements to be a fish (6):

• Live in water

• Gills are the primary respiratory organ

• Ectotherms and Poikilotherms

• Chordates & Vertebrates

• Fins for limbs

• Scales

Exceptions to requirements to be a fish:

• African lungfish is an obligate air breather

• Some sharks and tuna are endothermic

• Catfishes lack scales

• Hagfishes have no fins or vertebrae

How does life in water differ from life on land?

• 800x denser at sea level, causing reduced effects of gravity, buoyancy, and resistance to movement

• 60x more viscous than air, allowing large organisms to remain suspended and organisms to thrust against the water

• Reduced oxygen concentration 1% vs 20% by volume

• Dissolved compounds inside water, like salt or pollutants

• Light availability is much less, the photic zone is only about 200 m in open ocean, and much less in freshwater

• The specific heat of water is higher than air, causing less temperature fluctuations in both the short and long term

Functions of skin and scales (5):

• Physical protection

• Barrier against pathogens, such as microbial infections

• Mucous production

• Contains sensory cells

• Relatively impermeable barrier to water and ion diffusion, important for osmoregulation

Epidermis

• Outer layer of the integumentary system

• Contains blood vessels, nerves, sensory organs, and connective tissue 

• Thickness of skin depends on thickness of dermis

Why do scaleless fish tend to have thicker skin than scaled fishes?

Because they do not have scales to protect them

Dermis

• Inner layer of the integumentary system

• Generally thicker than epidermis

• Contains mucous cells, squamous epithelial cells, alarm cells, and chromatophores

Alarm cells

Cells that contain fluids with a chemical signal that alerts other fish other same species that there is danger when the fish's skin is broken

Chondrichthyes

cartilaginous fish, such as sharks and rays

Mucous

• Mostly glycoproteins (mucin)

• Threads of mucin hold water and give fish slimy feel

• May entrap or kill pathogens

• Hypothesized to be involved in water and ion regulation

• Decreases friction, helps lubricate

• Some fish produce toxic mucus

Hagfish slime

• Famous for producing a lot of slime using mucus and thread cells

• Mucus rapidly expands when it comes in contact with water

• May be used to suffocate prey, defense, or as protection from digestive enzymes

Placoid Scales

• Found in chondrichthyes

• Similar to teeth, dentine with pulp cavity that contains capillaries and enamel outer layer

• Pedestal with flattened top

• Do not grow, new scales are added as fish grows

Cosmoid & Modified Cosmoid scale

• Thick, bony scales that are similar to placoid and most likely arose from evolution of placoid, covered in cosmoid

• Cosmoid found in fossil coelacanths and fossil lungfish, modified cosmic scales found in living coelacanths and have no dentine layer, only two layers of bone and enamel

Ganoid scales

• Modified cosmoid scales, cosmine replaced with dentine, vitro dentine replaced by ganoine

• Rhomboidal in shape, peg and socket joint connects scales

• Form an armor for the fish, example is gar, or modified ganoid scales are scutes on sturgeons

• Big, thick, and tough

Cycloid scales

• First observed in primitive teleosts, such as minnows, trout and salmon, herrings

• Not made of enamel, bony layer and fibrous layer made of collagen

• Flexible, not hard

• Scales overlap like shingles

Ctenoid scales

• Found in most evolutionarily advanced species, and is one of most common

• Have ctenii, teeth-like projections from the posterior part of the scale which may contain enamel

• Found in blue gill, croaker, spot, large mouth bass

• Scales overlap

• Greater flexibility than armored fish, due to being thinner and lighter

Age Estimation with Scales

• Can be done with ctenoid, cycloid, and sometimes ganoid, but not placoid (b/c their scales don’t grow)

• Historically most used technique

• Estimation is not as accurate as otoliths, spines, or cleithra because they can become damaged or reabsorbed

• Still common due to tradition and no lethality, but tend to give underestimation of age

What is the role of the skeleton in fish?

• Structure and support

• Provides framework for the body

Why is osteology important for the study of fishes?

• Gives an understanding of form and function, such as locomotion and feeding

• Classification and evolution of species

• Fish diet studies

• Examination of fish populations over time

How are fish bones studied?

• Fleshing beetles

• Clearing and staining

• CT scanning

Cellular bone

connective tissue, made from osteocytes within lacunae, low minority of fish have this

Acellular bone

Bones that do not have osteocytes, majority of fish possess this 

Neurocranium

Protects the brain and sensory organs

Contains:

• Ethmoid

• Orbital - bones around the eyes

• Otic - enclosed ear chamber

• Basicranial - posterior portion og upper skull, forms passageway for spinal cord

Branchiocranium

Used for feeding, protection, and support of the gills

Contains: 

• Mandibular arch - forms upper jaw and parts of lower jaw

• Teeth

• Palatine and hyoid arches - bones in roof of mouth, parts of lower jaw, gill supports

• Opercular and branchial series - gill covers, arches, rakers, and pharyngeal teeth 

Mandibular arch region

Lower jaw consists of Meckel’s cartilage in chondrichthyans, covered by dentary in bony fishes

Examples of species with different teeth types

• Canine - Bowfin

• Villiform - Gars

• Molariform - Cownose rays

• Cardiform - largemouth bass

• Incisor - chimeras

• Teeth fused into beaks - parrotfishes

• Triangular cutting teeth - Sharks

• Pharyngeal teeth - “shell cracker”

Palatine and Hyoid Arches

• palatines frequently bear teeth

• suspensorium - series of bones that connects the lower jaw and opercular apparatus to the skull

Opercular and Brachial Series

• opercular apparatus - flat bones that cover and protect gills, involved in respiration and feeding

• brachial complex - inside throat, four pairs of gill arches, gill rakers, and pharengyal teeth patches

Pharyngeal Teeth

• attached to gill arches

• used to process food

• frequently observed in fish that eat mollusks

Postcranial Skeleton

• notochord - rodlike supporting structure in embryo of chordates that disappears after embryonic stage in most fish, such as lungfishes and sturgeons

Precaudal Vertebrae

anterior vertebrae bearing ribs extending posteriorly until reaching end of body cavity

Caudal Vertebrae

beginning with the first vertebra with elongated hemal spine and hemal canal with the caudal artery enters

Three types of intramuscular bones

epineruals, epicentrals, epileruals

Epurals

modified neural spines

Hypurals

enlarged hemeal spines

Pectoral Girdle

no attachment to vertebral column, attaches to back of skull

Cleithrum

part of pectoral girdle, used in age estimation for escoids 

Pelvic Girdle

• attachment structures for pelvic fins

• usually not attached to vertebral column

• sharks: cartilage that floats freely in muscle

Fins supported by what in chonrichthyctyes

ceratotrichia

Fins supported by what in bony fish

lepidotrichia

dorsal and anal fin rays and spines supported by

ptergiophores

Greater proportion of muscle mass is used for what in fish?

Locomotion

Why is fish muscle tissue relatively delicate compared to other vertebrates?

Due to reduced effects of gravity, the water supports their body mass

Why does muscle color differ among different species?

Myoglobin content, diet, genetics

Most of fish body mass is what muscle type?

Skeletal, which is striated and voluntary

Myomere

Post cranial skeletal muscle arranged in repeating segments, the pink part of a salmon filet, frequently used to ID juvenile and larval fish

Myosepta

Connective tissue that myomere attach to

Hypaxials

muscles in ventral half of the fish

Epaxials

muscles in dorsal half of fish

Red muscle

slow aerobic oxidation, if you are going on a 10 mile run, blue fin tuna possess a lot of this because they are always on the move

White muscle

fast, anaerobic glycolysis, fast burst of speed, high content in sedentary species, but all fish contain a majority of white muscle over red

Pericardial sac

the sac in which the heart sits in

Fish have a _____ heart size relative to their body, why?

small, because fish are ectotherms and do not need much energy

Flow of blood through the heart from the body to the gills

Sinous venousus, atrium, ventrical, bulbous arteriosis

bulbous arteriosis

elastic chamber that dampens pulsed into a more continuous flow so that gills are not damaged

Most fish have a ______ loop system for their circulatory

closed, which means it goes through the heart once during a complete circulation

Relative to body size, blood volume is ____ in teleosts compared to Chondrichthyes

Blood production and amount for lampreys

8-20% of body weight, hagfish produce blood in mesodermal envelope around gut, lampreys synthesize it from fatty tissue

Elasmobranchs blood production and amount

4-8% of body weight, synthsized in esophagus, spleen, and around the gonads

Osteichthyes

3-7% of body weight is blood, produced in kidney and spleen

more active fish tend to have more, smaller RBC’s, why?

because there is a shorter diffusion distance and they take up greater surface area, which means more efficient oxygen uptake at the gills

Many species do not respond to alarm cells until they are a

juvenile

Juvenile fish go through a transition called

metamorphosis

Cycle of smoltification

Alvein, parr, smolting juvenile, adult salmon

Changes that occur during smoltification

• change in color, loss of parr markings

• increase in gas in gas bladder

• increase in hemoglobin to account for shift from stream to ocean

• become more streamlined

• allows more chloride cells to develop in the gills, which ensures that they are not hypo osmotic in marine water

• brought on by changes in thryoid hormone, photoperiod, and water temp

Flatfish juvenile to adult

start out as a normal looking larvae, but part of the head and eyes rotate to one side of the face

Why is bigger better for a juvenile fish?

• reduced risk of starving

• better tolerance for extreme environmental occurances

• compete better for resources

• avoid predation

Larval stages of fish

yolk sac - still reliant on yolk sac for nutrition, ends when sec absorbed

reflexion - start of outside feeding, development focused on head and tail regions

flexion - development of notochord

postflexion - fins begin to develop

metamorphosis - loss of larval charactersistics and begining of juvenile characteristics

How does countercurrent exchange maximize oxygen uptake?

it ensures blood with lower oxygen is always in contact with water with high oxygen, water moves in one direction to ensure oxygenation