The Perch: Inside and Out
A guided dissection and discussion of a perch.
Oren Pazgal
4/9/14
Vu-PAP Bio-1
Objectives
- Students will be learning about the external and internal anatomy of a perch.
- Students will focus on the organs, structures, and functions of the circulatory system.
- Students will also understand the ecological role of the perch.
The genus Perca
Perches are a type of bony fish, which means that they have a rigid endoskeleton as well as scales covering their entire bodies. There are different species of perch in different parts of the world, but they all possess some common characteristics, as befits organisms in the same genus. A typical perch has a lifespan of 15-25 years, and a perch reaches sexual maturity at approximately 2-4 years of age. Perch only reproduce once a year in spring or early summer, but when they do reproduce all of the females release their eggs which settle to the bottom of whatever body of water they are inhabiting. Then the males release their sperm all at once, so that eggs can be fertilized by random males and achieve greater genetic diversity, which encourages natural selection. The eggs hatch around three weeks after fertilization, at which point they are known as prolarvae. The prolarvae mature and grow to adulthood, and so the cycle continues.
Predators
Perches serve as a food source for many larger fish, including but not limited to: several species of bass and fish-eating birds, bluefish, and walleye.
Habitat
Different species of perch are found all over the world, but all live in fresh water. Examples of locations where perch are common include the Great Lakes of North America and Lake Balkash in Kazakhstan, but they have been introduced to habitats across the globe. Though there are many close relatives of the perch that inhabit salt water, they actually belong to different genera. Even though these fish might have "perch" in their names, there are very few species that actually belong to the genus Perca.
Prey
Perch tend to eat aquatic insects and mussels when they are young, and as larvae they prefer to consume algae. However, adult perch often consume smaller fish, and they are not particularly picky about what kind. This is what makes them especially harmful to local ecosystems that they are not native to.
Ecology and Evolution
Since perches have such a varied diet from the prolarvae stage to adulthood, they function as both primary, secondary, and occasionally even tertiary consumers in their ecosystems. To help perch accomplish the task of consuming its food sourcesthey have evolved specialized teeth called palatines to eat smaller fish more easily. Not only that, but the perch has evolved gill rakers in the gills, which serve to filter out zoo-plankton from the gills and send them straight down the esophagus.
Below is a cladogram of the cursory evolutionary relationships of the genus Perca and other ray-finned fishes:
Dissection
Labelled Guide
The picture above shows a labelled diagram of many pertinent organs and features of a perch, both internal and external.
Before
Note the anal, caudal, dorsal, pectoral, and pelvic fins attached to the fish's body. The eyes and gill slits are also visible towards the anterior end of the fish.
After
A square hole has been cut out of the middle of the fish, exposing the gills, swim bladder, and much of the digestive and excretory systems of the perch.
***The swim bladder is what allows the fish to retain its buoyancy while swimming.
Highlight: The Circulatory System
Although the circulatory system cannot easily be seen in the above pictures, it performs some absolutely vital tasks for perches' (and many other organisms') survival. The circulatory system is responsible for pumping blood throughout the body and carrying oxygen and other necessities to the body's cells. A perch's circulatory system consists of a single ventricle and atrium (the heart), an aorta, and all of the blood vessels in the body. In a perch, the circulatory system consists of only a single loop. The ventricle pumps out blood which then travels through the arteries to the gills, where the blood is oxygenated. The blood then moves through the long aorta and then through the capillaries that run throughout the body, supplying oxygen to all of the cells. The newly deoxygenated blood returns to the heart through the veins and enters the atrium before it is sent out on the loop again.