AP Bio Squad P2-3a: AP Biology Final Project: Fish Dissection

Fish (Perch) Dissection

Background Information

The name of ‘perch’ applies to more than 6000 different species. They are found in the waters of Eurasia and North America. Names of the most common species include yellow perch, European perch, and spangled perch. Although their appearances vary by species--think golden perch and silver perch--they have an average size of about 10-20 inches and are characterized by a strong, long spine. Perch are all freshwater fish, so they are found in lakes, ponds, and rivers. Their diet may vary by size. Plankton and insect larvae are included in the diets of most, but larger perch may consume smaller fish as well.

Like most fish, perch breathe with the movement of water into and out of the gills. Water is taken in through the mouth and forced through the gills. The thin walls of the gills pass dissolved oxygen to the bloodstream, and the rest is forced out of the fish.

Perch are usually characterized by distinctive stripes along their sides. The yellow perch has dark black bands across its sides while the remainder is yellowish in color. The European cousin of this species is similar, just darker in tinge.

Major Internal and External Anatomy

Maxilla: the upper jaw, fixed and immovable, which serves as a clamping base for the lower jaw

Mandible: the lower jaw, movable to grasp and obtain food

Operculum: covers and protects gills, regulates the flow of water over gills

Gills: respiratory and excretory organs each formed of two layers of filaments; they enable water to exchange oxygen and ammonium as it circulates over the gills

Anal fins: stabilize the back region of the fish during motion

Urogenital pores: opening common to the genital and urinary tracts allowing the evacuation of gametes and urine

Liver: viscera that secretes bile, among other substances; bile helps digestion

Heart: muscular organ helping blood to circulate

Swim bladder: fills with oxygen; closed sac that maintains the fish at one or more pressure levels throughout the sea by secretion and absorption of gas

Stomach: dilated section of the digestive tract preceding the intestine; receives food to be digested

Intestines: section of the digestive tract between the stomach and the anus where absorption of nutrients is carried out and waste is transformed into fecal matter

Gonads: testes that produce sperm in males, ovaries that produce ova in female

Incision Guide

The bony flap that covers the gills on either side of the fish's head are called the opercula. Use scissors to remove the opercula that is on the upwards facing side when the fish is laid flat.

Take note of the spacing between the gills. Then, cut out a single gill with the curve gill arch and the soft gill filaments attached.

If needed, secure the fin to the dissecting pan with pins. Then, use a scalpel and/or scissors to make a rectangular cut that extends from the very end of the operculum to the beginning of the curve at the rear of the fish or the anal fins. Carefully remove this flap, ensuring it is only skin and muscle with no internal organs attached.