Question

1. What is the purpose of the “spines” on its dorsal fins?
2. Spiny dogfish sharks are considered to be vulnerable to overfishing. How are the spiny dogfish sharks managed in order to provide sharks for dissection as well as human consumption?
3. What is meant by fusiform? How do sharks use it to their advantage?

Answer 1

A dorsal fin is a fin located on the back of the marine and freshwater vertebrates such as fishes. Dorsal fin is made of dense, fibrous connective tissue without bones or cartilage. Its size and shape vary between ecotypes. The main purpose of dorsal fin is to maintain the animals against rolling and help in sudden turns. Spiny dog fish also known as piked dog fish. Spiny dogfish sharks are gregarious and travel in schools of hundreds to thousands of individuals and following cool waters. Two large, sharp, mildly poisonous dorsal spines are located in front of each dorsal fin. The first dorsal fin of the spiny dogfish is larger than the second dorsal fin.The spiny dogfish uses its spines defensively by curling up to its body and stricking at an enemy. It is considered as the most abundant living shark species in the ocean, but are harmless to humans.

In general, spiny dog fish posess little threat to humans because of the presence of spine on dorsal fin that can results wound if not handled carefully. The spiny dog fish has a dorsal fin.The anterior dorsal fin is larger than the posterior dorsal fin. The spines carry poison secreated by glands at their base. The caudal fin is divided into two lobes such as, a smaller dorsal lobe and a larger ventral lobe and this type of tail is known as heterocercal tail. Both the spiny dogfish and the smooth dogfish are edible. However, the spiny dogfish is in cool water that feeds mostly on small crabs, lobsters and other shell fish this gives their meat a codfish style taste. The spiny dogfish population is in trouble, because there was a huge commercial fishery.

Fusiform means having a spindle like shape that is wide in the middle and tapering at both ends. Sharks have fusiform body with well developed paired fins and a powerful heterocercal tail. This fusiform body shape is exceedingly helpful because it minimises drag and it enable shark to swim efficiently while using the least amount of energy possible.