This module introduces the study of fishes, covering their definition, characteristics, ancestry to humans, and habitats.
Total learning time: 9 hours / 1 week.
Prerequisites: None.
Learning Outcomes
Familiarize with the definition of fishes.
Know the general and basic descriptions of fishes.
Gain concept on how the fishes served as ancestors to humans.
Learn the interactions between fishes, other organisms, and their environment.
Indicative Content
Definition and description of fishes
Excluded topics in ichthyology
Importance of studying the fishes
Fish physiology and biochemistry
Fish as ancestors to men
The first fishes to be recorded
Major lines in ichthyology
Fish classification and anatomy
Fish evolution and genetics
The natural history and ecology of fishes
Fish habitats
Areas / habitats of fishes
Water and how the fishes live
Fish conservation
Notable organizations involved in fish conservations
Pre-assessment Questions
Why do you think it is important to study the fishes?
What makes one fish different from the others?
In your own words, describe the most suitable environment in which the fishes could thrive and reproduce.
Content: Ichthyology Definition and Description
Ichthyology is defined as 'the study of fish' or 'that branch of zoology dealing with fish'.
A fish is a vertebrate with gills, a body covered with scales, and lives in the water.
Some species can leap out of the water and glide using their fins.
Some species can live out of the water for some time using auxiliary breathing organs.
Some species do not have scales.
'Fishes' refers to more than one type (or species) of fish.
'Finfish' refers to sharks, some rays, and bony fishes.
'Scale fish' refers to fish bearing scales.
Ichthyology has a long history dating back to ancient civilizations due to fish being both fascinating and a food source.
This interest has generated heterogeneous information, including taxonomic data, zoogeography, behavior, food, predators, and environmental tolerances.
The vast amount of information has led ichthyologists to specialize in either global or local studies.
General Characteristics of Fishes
Cold-blooded (poikilothermic)
With backbones
With gills
With fins
Primarily dependent on water
Fish Anatomy and Physiology
Unlike mammals, fish are cold-blooded (poikilothermic), meaning their body temperature is influenced by their environment.
True fish have a backbone and fins.
Most breathe with gills and have scales.
Fish began to evolve about 480 million years ago.
There are approximately 33,600 known species of fish.
Fins provide balance and help with propulsion and steering.
Most fish have single fins along the centerline (dorsal and anal fins) and paired fins.
The caudal fin (tail fin) is the main fin for forward movement.
Dorsal and anal fins help with balance.
Paired fins help with steering and hovering.
Some species, like pufferfish, do not have scales.
Scales can be jagged or smooth.
Fish secrete mucus to protect against infection and reduce friction.
Gills extract oxygen from the water.
Gills contain capillaries that filter oxygen into the blood.
The operculum (gill cover) protects the sensitive gills.
Gills are also important for excretion of waste products, particularly ammonia.
The swim bladder or air bladder helps fish move up or down in the water.
Sharks and rays (elasmobranchs) do not have a swim bladder.
Many fish have excellent vision and can see colors.
Fish have nostrils to detect odors in water.
Fish may or may not have teeth, depending on the species.
The lateral line is a sensory organ that detects underwater vibrations.
Excluded Topics in Ichthyology
Mammals (whales, seals, porpoises)
Reptiles (turtles, snakes, crocodiles)
Invertebrates (clams, shrimps, lobsters)
Marine Mammals
Marine mammals breathe air through lungs, are warm-blooded, have hair, and produce milk.
They live most or all of their lives in or near the ocean.
Classified into cetaceans, pinnipeds, sirenians, and marine fissipeds.
Reptiles in Marine Habitats
Reptiles evolved from aquatic amphibians about 260 million years ago.
Only a few reptile groups re-entered the oceans, such as sea snakes and sea turtles.
Major reptile groups have members that enter marine habitats.
Marine Invertebrates
Invertebrates lack backbones and rely on other support strategies.
Over 98% of species on Earth are invertebrates.
Common marine invertebrates include sponges, cnidarians, marine worms, mollusks, arthropods, echinoderms, and hemichordates.
Importance of Studying Fishes
Needed for information concerning the species.
Commerce.
Recreation.
Fish are classified by comparing proportional measurements and examining features such as fin spines, scales, teeth, and gill rakers.
Coloration is important, with variations between males, females, and juveniles.
Genetics plays an increasing role in fish taxonomy, comparing DNA of the study animal to related species.
Knowledge of fish diversity, distributions, habitat requirements, and life histories are essential for fisheries management and conservation.
Many fish groups are still to be worked on, and many areas have not been adequately surveyed.
The larval stages of many fishes are poorly understood.
Numerous fish species remain undescribed.
Future surveys will likely yield new fish discoveries.
Fish Physiology and Biochemistry
Physiology studies how an animal's body functions and responds to its environment.
In fishes, physiology studies often involve measuring factors such as swimming performance, heart rate, oxygen consumption, body chemistry and hormones, and survival under a variety of conditions.
Knowledge of fish physiology is essential for managing fish populations, especially in modified waterways.
Scientists use swim tunnel respirometers to measure the metabolic rate of fish at a range of temperatures.
Aerobic scope is the difference between a fish’s resting and swimming metabolic rates.
A steelhead's aerobic scope becomes very small at high water temperatures.
Fish are in trouble when their aerobic scope approaches zero because their hearts cannot pump enough to support swimming, eating, or escaping predators.
Physiological studies can provide valuable insights to inform fish conservation and management.
These include how fishes respond to and tolerate a range of environmental conditions, and how fish bodies and internal processes change throughout different life stages.
Physiological tools are particularly valuable for improving predictions of how fish populations will respond when faced with novel conditions.
Physiological tools that measure the responses of individual fish to environmental changes can be combined with population monitoring to actually explain why population characteristics change, and can therefore be used to predict population responses to novel conditions in nature.
Scientists have learned that marine species living near the equator are more susceptible to warming water temperatures due to global climate change than fish living at higher latitudes.
Global climate change and rising human water demands make balancing the health of wildlife and the requirements of growing human populations increasingly challenging.
Fish External Anatomy and Major Organs
Fish are cold-blooded, have fins, and a backbone.
Most fish have scales and breathe with gills.
Approximately 22,000 species of fish began evolving 480 million years ago.
Fins are appendages used by the fish to maintain its position, move, steer and stop.
They are either single fins along the centerline of the fish, such as the dorsal (back) fins, caudal (tail) fin and anal fin, or paired fins, which include the pectoral (chest) and pelvic (hip) fins.
The dorsal and anal fins primarily help fish to not roll over onto their sides.
The caudal fin is the main fin for propulsion to move the fish forward.
The paired fins assist with steering, stopping and hovering.
Scales in most bony fishes are either ctenoid or cycloid.
Ctenoid scales have jagged edges, and cycloid ones have smooth rounded edges.
Most fishes also have a very important mucus layer covering the body that helps prevent infection.
The gills are the breathing apparatus of fish and are highly vascularized.
An operculum (gill cover) that is a flexible bony plate that protects the sensitive gills.
Water is inhaled through the mouth, passes over the gills and is exhaled from beneath the operculum.
Fish can detect color.
Paired nostrils, or nares, in fish are used to detect odors in water and can be quite sensitive.
The mouth's shape is a good clue to what fish eat.
The lateral line is a sensory organ consisting of fluid filled sacs with hair-like sensory apparatus that are open to the water through a series of pores.
The lateral line primarily senses water currents and pressure and movement in the water.
The vent is the external opening to digestive urinary and reproductive tracts.
Climate Change and Fish populations
Resolving the effect of climate change on fish populations is complicated, because climate change affects a multitude of environmental factors that may affect various processes at different levels of biological organization.
Statistical correlations do not necessarily indicate underlying processes.
Fish as Ancestors to Men
Human hands likely evolved from the fins of Elpistostege, a fish that lived more than 380 million years ago.
One of the most significant events in the history of life was when fish evolved into tetrapods, crawling out of the water and eventually conquering land.
To complete this transition, several anatomical changes were necessary. One of the most important was the evolution of hands and feet.
The First Fishes to be Recorded
When the Devonian period dawned about 416 million years ago the planet was changing its appearance.
Early placoderms fed on mollusks and other invertebrates, but later species developed into ferocious, fish-slicing monsters measuring up to 33 feet (10 meters) long.
The Devonian ancestors of fishes living today belonged to two main nonarmored groups.
The cartilaginous fish later gave rise to sharks and rays.
The second group, the bony fish, were covered in scales and had maneuverable fins and gas-filled swim bladders for controlling their buoyancy.
The bony fish included lobefins. Named after the thick, fleshy base to their fins, lobefins are credited with the giant evolutionary stride that led to the amphibians, making lobefins the ancestors of all four-limbed land vertebrates, including dinosaurs and mammals.
Fish Habitats
Fish might be found in water scarcely deep enough to cover their backs, or they might swim in unfathomable depths.
Each species of fish goes through different cycles at various times of the year and eats different foods.
Individual and species needs and preferences present too complicated an equation for people or computers to master.
Areas / Habitats of Fishes
Each fish species has its specific habits, especially when it comes to foods and their habitats.
You can identify these fish groups based on the foods they eat, whether they are carnivores, herbivores, or even omnivores.
Fish can look for their prey together on a school of minnows, migrating frogs, and hatching insect larvae because they are rich in protein.
Carnivores are meat-eating fish and dependent on foods with higher protein. Without protein intake, they would become malnourished and die.
Herbivores are plant-eating fish that are fed on cucumber, vegetables, algae, and algal flakes.
Lastly, omnivores are not picky with foods because they can eat both meat and plants. Since they tend to be unmindful of their food intake, that’s the reason why they kept themselves in trouble, as they overfeed themselves.
Fish are smart enough to ambush their prey using their markings as their cover. They can live in weeds, rocks, logs, and rocks to make them less visible to their prey. When their prey unknowingly comes near, that’s the time where they’ll start to attack.
Generally, fish can swim in more shallow waters with low light during the earlier spring and summer, where they send themselves deeper to find a cooler place to stay, but not at the bottom because there’s little oxygen.
Fish prefers the low light condition. Fish like catfish and crappie would feed in whatever weather condition, although for anglers, it’s better to fish after a thunderstorm and during gentle rain because fish tend to rise above the waters.
Where do fish live?
Antarctic waters below freezing
Hot springs of more than 40°C
Soft, fresh water to water saltier than the seas
5 km above sea level
11 km beneath
Water is the fish’:
Highway
Byway
Communications
Medium
Nursery
Playground
School
Room
Bed
Board
Drink
Toilet
Grave
Water and How the Fishes Live
Dissolved oxygen - Each type of fish living in the water requires a different amount of dissolved oxygen to live. For example, Northern Pike cannot survive in less than about 6 milligrams of dissolved oxygen per liter of water (6 mg/L). If dissolved oxygen levels decrease to about 3-4 mg/L, even the strongest fish may suffocate.
Dissolved salts - Salinity is important in particular as it affects dissolved oxygen solubility. The higher the salinity level, the lower the dissolved oxygen concentration. Oxygen is about 20% less soluble in seawater than in freshwater at the same temperature. This means that, on average, seawater has a lower dissolved oxygen concentration than freshwater sources. The effect of salinity on the solubility of dissolved gases is due to Henry’s Law; the constant used will changes based on salt ion concentrations.
Most aquatic organisms can only tolerate a specific salinity range. The physiological adaption of each species is determined by the salinity of its surrounding environment. Most species of fish are stenohaline, or exclusively freshwater or exclusively saltwater. However, there are a few organisms that can adapt to a range of salinities. These euryhaline organisms can be anadromous, catadromous or true euryhaline. Anadromous organisms live in saltwater but spawn in freshwater. Catadromous species are the opposite – they live in freshwater and migrate to saltwater to spawn. True euryhaline species can be found in saltwater or freshwater at any point in their life cycle. Estuarine organisms are true euryhaline.
Salinity tolerances depend on the osmotic processes within an organism. Fish and other aquatic life that live in fresh water (low-conductivity) are hyperosmotic. Hyperosmotic defines a cell’s ability to eliminate water and retain ions. Thus, these organisms maintain higher internal ionic concentrations than the surrounding water. On the other side of the spectrum, saltwater (high-conductivity) organisms are hypoosmotic and maintain a lower internal ionic concentration than seawater. Euryhaline organisms are able to adapt their bodies to the changing salt levels. Each group of organisms has adapted to the ionic concentrations of their respective environments, and will absorb or excrete salts as needed. Altering the conductivity of the environment by increasing or decreasing salt levels will negatively affect the metabolic abilities of the organisms. Even altering the type of ion (such as potassium for sodium) can be detrimental to aquatic life if their biological processes cannot deal with the different ion.
Light penetration - Light compares a complex of external and ecological factors, including colour spectrum, intensity and photoperiod. Light characteristics are very specific in an aquatic environment and light is extremely variable in nature. Receptivity' of fish to light profoundly changes according to the species and the developmental status. Specific photoreceptor cells are present in both eye and pineal. If it is easy to change the light in experimentation and to observe the effects on fish growth, it is much more difficult in nature to make such determinations. In larvae, many studies have been dedicated to the influence of intensity and photoperiod on growth: generally, species need a minimal threshold intensity to be able to develop normally and grow. This is probably related to the aptitude to localize, catch and ingest prey. Light is also indispensable for body pigmentation, an important phenomenon involved in early development and growth. Too intense light can be stressful or even lethal. A few species are able to develop and grow at very low intensities or, sometimes, in the absence of light. Generally, long daylength improves larval rearing quality. The synergistic effect offood availability-daylength' appears to be determining at this stage. In older fish, there is very little information about the influence of light `quality' but more about intensity and much more about photoperiod. Light intensity effects are not so clear and depend on the species and the experimental procedures: it is probably not an important factor for growth stimulation. Daylength appears much more important. Many species, including both marine species and salmonids, react to photoperiod treatments and long daylength stimulates growth.
Temperature - Water consists of two parts hydrogen for every one-part oxygen. However, this oxygen is not used by the fish. They breathe the excess oxygen in the water. High barometric pressure forces more oxygen into the water than low barometric pressure. Also, wave action or current exposed more surface area, thus raising the oxygen content.
Growing plants give off abundant oxygen. Cold water has the ability to hold more oxygen than warm water. Hot summer temperatures can heat water so it won’t hold enough oxygen to maintain fish life. Oxygen content and water temperature go hand in hand; just like a reel goes with your fishing rod Fish are cold blooded and take on the temperature of their surroundings.
Toxic substances - Toxic contaminants end up in our state's waterbodies in different ways. Industrial and municipal discharges, agricultural practices, and storm water runoff can all put harmful substances into the water. Rain can also wash chemicals from the land or air into streams, rivers, lakes, and Puget Sound. Fish absorb contaminants such as polychlorinated biphenyl (PCBs), Polybrominated diphenyl ethers (PBDEs), dioxins, and chlorinated pesticides from water, sediments, and the food they eat. In contaminated areas, bottom-dwelling fish are especially likely to have high levels of these chemicals because these substances settle to the bottom where the fish feed.
Concentrations of disease organisms
Opportunity to escape enemies
Fish Conservation
Wise use and management of fish resources for the benefit of man through the following:
Fisheries statistics
Fisheries technologies and marketing
Laws
Population manipulation
Fish culture and stocking
Environmental improvement
Notable Organizations Involved in Fish Conservations
Fish Division, UN Food and Agriculture Organizations