Chub mackerel
Encyclopedia
The chub mackerel, Scomber japonicus, also known as the Pacific mackerel or blue mackerel and sometimes referred to as a "hardhead" or "bullseye", closely resembles the Atlantic chub mackerel
.
, which the "true mackerels" in the Scomber genus lack. But it is not necessary to open the fish to identify it for there is a characteristic color difference between them, the Atlantic being silvery-sided below the mid line, whereas the lower part of the sides of the hardhead (otherwise colored somewhat like the Atlantic) are mottled with small dusky blotches, and the chub has a larger eye than the Atlantic. Less obvious differences are that the dorsal fin
s are closer together in the chub and that there are only 9 or 10 spines in its first dorsal fin instead of 11 or more, which is the usual count in the Atlantic mackerel. In most species the mackerel is known to travel in large schools.
s and Sagittae that the mackerel had taken at the same time and place, while specimens taken at Woods Hole had dieted chiefly on copepod
s, to a less extent on amphipods, salp
s, appendicularians, and young herring
. They follow thrown bait as readily and bite quite as greedily as Atlantic mackerel do. Their breeding habits have not been studied.
. Absent from the Indian Ocean
except for South Africa
from KwaZulu-Natal
to Western Cape
. Replaced by the closly related Atlantic chub mackerel
in the Atlantic.
Atlantic chub mackerel
Atlantic chub mackerel is a pelagic schooling species of mackerel found in the Atlantic Ocean, also in the Mediterranean Sea and the Black Sea. It was described as subspecies of the Chub mackerel Scomber japonicus colias....
.
Identification
Most important of the differences, anatomically, is the fact that the hardhead has a well-developed swim bladder attached with the esophagusEsophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, which the "true mackerels" in the Scomber genus lack. But it is not necessary to open the fish to identify it for there is a characteristic color difference between them, the Atlantic being silvery-sided below the mid line, whereas the lower part of the sides of the hardhead (otherwise colored somewhat like the Atlantic) are mottled with small dusky blotches, and the chub has a larger eye than the Atlantic. Less obvious differences are that the dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s are closer together in the chub and that there are only 9 or 10 spines in its first dorsal fin instead of 11 or more, which is the usual count in the Atlantic mackerel. In most species the mackerel is known to travel in large schools.
Habits
Chub mackerel school like Atlantic mackerel, and their feeding habits are much the same, eating the same species of pelagic crustaceanCrustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and Sagittae that the mackerel had taken at the same time and place, while specimens taken at Woods Hole had dieted chiefly on copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s, to a less extent on amphipods, salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s, appendicularians, and young herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
. They follow thrown bait as readily and bite quite as greedily as Atlantic mackerel do. Their breeding habits have not been studied.
Distribution
It is widespred in the Indo-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
. Absent from the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
except for South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
from KwaZulu-Natal
KwaZulu-Natal
KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....
to Western Cape
Western Cape
The Western Cape is a province in the south west of South Africa. The capital is Cape Town. Prior to 1994, the region that now forms the Western Cape was part of the much larger Cape Province...
. Replaced by the closly related Atlantic chub mackerel
Atlantic chub mackerel
Atlantic chub mackerel is a pelagic schooling species of mackerel found in the Atlantic Ocean, also in the Mediterranean Sea and the Black Sea. It was described as subspecies of the Chub mackerel Scomber japonicus colias....
in the Atlantic.