Lab - Dogfish Shark Basics

Question 1

What type of body shape does the dogfish shark (and other fish) have? And why is that shape unfortunate for the people studying it?

Answer 1

Fish have a streamlined or fusiform body shape, which unfortunately makes it hard to externally discern where the head ends and the rest of the body begins

Question 2

Describe the regions of the dogfish shark

Answer 2

Head (including branchial region)m trunk (extending to cloaca) and tail (cloaca to caudal)

Question 3

What are the scales on the dogfish called and what do they feel like? What other part of the fish are they related to?

Answer 3

Placoid scales. They feel like sandpaper. Placoid scales are plates emebedded in the dermis of the skin with one sharp point facing caudally. These resemble teeth and teeth may actually be derived from scales

Question 4

What is counter shading?

Answer 4

Counter shading is dorsal (dark) to ventral (light) colouration of most fishes that helps to keep them hidden in the water

Question 5

Why is the dogfish shark sometimes called the spiny dogfish?

Answer 5

The dogfish shark has spines on the anterior margin of each dorsal fin

Question 6

Name and describe the fins of the dogfish shark

Answer 6

Anterior and posterior dorsal fins, paired pectoral fins and paired pelvic fins. Males have claspers on their pelvic fins

Question 7

Name and describe the parts of the head of a dogfish shark

Answer 7

The dogfish has immovable eyelids. at each corner of the mouth is a labial pouch containing a labial fold. The teeth are modified scales, arranged in rows. On the top of the head are two tiny holes which lead to the inner ear called the endolymphatic pores

Question 8

How many external gill slits does the dogfish shark have?

Answer 8

5

Question 9

Describe the spiracle

Answer 9

It is a reduced gill slit caudal to the eye. Water can enter the spiracle when the mouth is occupied by prey. There is a reduced gill on the spiracular valve (which covers the spiracle) called the pseudobranch

Question 10

Describe the sensory system on the head of the dogfish shark?

Answer 10

Patches of pores on the head region belong to the ampullae of lorenzini, which are sensory structures that can detect a small electric field and sense the presence of non-visible prey. This system is derived from the lateral line system

Question 11

Describe the cloaca

Answer 11

A multi-purpose orifice for storing waste and reproductive materials. In the cloaca is a papilla (for urine in females and urine/sperm in males). The opening of the digestive system into the cloaca is called the anus

Question 12

Name the parts labelled 1-11. What are the pores at 12 referred to as?

Answer 12

1. Spiracle
2. Lateral line
3. Dorsal fin
4. Heterocercal caudal fin
5. Pelvic clasper
6. Pelvic fin
7. Pectoral fin
8. External gill slits
9. Nare/nostril
10. Labial pouch
11. Rostrum
12. Ampullae of Lorenzini