Blue cod

The blue cod (Parapercis colias) is a temperate marine fish of the family Pinguipedidae. It is also known variously as Boston blue cod, New Zealand cod, sand perch, or its Māori names rāwaru, pākirikiri and patutuki. It is exclusively found in New Zealand in shallow waters around the rocky coasts to a depth of 150 m, though it is far more common south of Cook Strait. It is bluish green to blue-black above with white toward the belly. Large examples are usually greenish blue in colour, while smaller ones are blotched in varying shades of brown. An adult may grow to 60 cm in length and weigh from 1.0 to 3.0 kg. It feeds mainly on small fish and crabs. Blue cod is territorial. Spawning takes place in southern spring. Blue cod can also change sex from female to male. It is a plump fish which produces good fillets, but it has a very low oil content. It can be served battered, crumbed, pan-fried, or baked. It is an important recreational species in the South Island and is commercially harvested. Blue cod populations are managed sustainably under New Zealand's fisheries quota management system, although are becoming scarce in some small areas due to fishing pressure. Annual catch range is between 2,000 and 2,500 tonnes. Parapercis colias are protogynous hermaphrodites, which means they have both female and male reproductive organs at the beginning and some females change sex to males later in their life. P. colias is a marine bottom dwelling fish that is found in coastal New Zealand waters. Their colouring varies on age and sex. Juveniles start off being generally pale in colour and have two long dark stripes along the sides which will turn brown and barely distinguishable when they become middle-sized fish. As they mature with a body length over 25 cm, both sexes would have a blueish-grey dorsal with a white underside. Females have a tinge of orange and there is a trend for them to become green when they grow larger. Brownish pigments can be found at the base of pectoral fin. On the other hand, adult males have distinctive blue-grey colour coat with greenish sides and a golden brown line can be found above each eye. Body length of P. colias is about 30–40 cm in general, but can up to 60 cm and their weight is 0.8-1.5 kg in general, but can up to 3 kg. Males tend to be larger than females. They can live up to 32 years old. Heads of P. colias are prominent and rounded with scales. They have a plump shaped body covered with firm scales. Above their non expanded cheeks are two large lateral eyes which can be rotate independently, this allows them to see almost everywhere around them. P. colias possess terminal mouth with bulbous lips. Their pelvic fins are generally placed forward on the throat with brown dots appear underneath it. There is a single horizontal stripe where ten to twelve scales above across their side of the body. The first part of their dorsal fin is small and short, followed by fins with five short spines. In contrast their second dorsal is long. A key used in an article of Cantwell can distinguish P. colias from other parapercids. Key features are listed below: Other characters of detailed skeleton structures (osteology) of Parapercis species can be found in an article written by Gosline. Swimming bladder is usually present in osteichthyids, it helps the fish to stay at a certain water pressure level (depth) without spending more energy. Swimming bladder in P. colias are absent. They will automatically sink to the sea floor if they stop swimming; therefore, they are called bottom-dwelling or sedentary bottom-hugging species. Their body shape of having a flattened abdomen indicates this as well. Normally, P. colias use their pectoral fin to swim, their body muscles and tails fin are only involved in swimming when a sudden burst or speed is needed, this type of swimming character is called labriform. As a result, their pelvic fins, used as props when they are resting on the seabed, are reduced and thicken. Due to their nature of being bottom-dwelling species, sand can clog their gills when they are resting. To remedy this, P. colias often hold their breath and open their mouths for a long interval like having a yawn to take good gulps of air every now and then. Speaking of having a yawn, if you look closely you will notice that P. colias do not have palatine teeth and only have small teeth; however, you would not want to feel their sharp and well developed pharyngeal teeth near their throat like their prey. There are some other detailed morphological characteristics inside the body of P. colias that determine their taxonomy, such as the presence of a lentiform body (an ocular vascular structure) and others, are mentioned by Eastman.