Fish characteristics

Preview
Although there are hundreds of fish species, it is possible to divide them into three distinct fish groups. It is also possible to summarise some general characteristics of fish:

Jawless fish Cartilaginous fish Bony fish Breeding patterns Habitat Age Fisheries Shellfish Aquaculture

top

	Lampreys
	Hagfish

Lampreys are found in freshwater lakes and streams as well as in salt water. They are a delicacy for Maori tribes in Wanganui and Waikato who know them as tuna korokoro.

The lamprey

Hagfish
Hagfish, or blind eels, are found only in salt water and feed mainly on dead fish. Although they are disliked by fishers because of the large amounts of slime they give off, blind eels, or tuare, are a traditional Maori delicacy. They are unusual fish as they are hermaphrodites. They produce only sperm or eggs at any one season, but they can produce sperm one year and eggs the next.

top

Cartilaginous fish
Cartilaginous fish include the sharks, skates and rays. Although these look different, they have many features in common. None of them have any true bone - their skeleton is made of cartilage.
They have strong jaws and their mouth is on the underside of the body, and their eyes are on top. They cannot see food as it enters their mouth. Some sharks solve this problem by touching their food briefly with their nose first. Some also use a powerful electrosensory system.

This diagram details the external characteristics of sharks.

Sharks, skates and rays usually have a rough skin, a bit like sandpaper, and have five to seven pairs of external gill openings. Chimaeras or ghost sharks are smooth-skinned and have only one pair of external gill openings. Fertilisation is internal and this group of fish produce few offspring. Reproduction is by:

1	The female laying fertilised eggs
2	The female bearing eggs which hatch internally, giving live birth
3	Live birth with the young shark attached by placenta.

top

Bony fish
Bony fish are often regarded as "true" fish. This group includes most of the fish we are familiar with, such as snapper, groper and gurnard. They have a bony skeleton and a single pair of external gill openings. The mouth is generally at the front of the body and they have a tail fin, with the top and bottom portions nearly the same size. Internally, the intestine of the bony fish is a relatively short tube.

This diagram details the external characteristics of a generalised bony fish.

Bony fish reproduce by external fertilisation of eggs. The female generally produces a large numbers of eggs and releases them into the water. The male releases sperm, normally called milt, into the water. The milt fertilises eggs it comes into contact with.

Breeding patterns
Fish of different types have different breeding patterns. Most come together in "schools" during the breeding season. Some pair off and a few are capable of self-fertilisation. Some fish, like salmon, leave the ocean and deposit their eggs in freshwater streams. Others, like some freshwater eels, spend their adult life in fresh water and migrate to sea to breed.

top

Habitat

Fish adapt to their environment, so different species often develop similar features and adaptations. For example, many deepwater species have common features like big eyes and dark colouring. Most fish are either wholly fresh water or wholly marine, though some spend parts of their lives in both environments.

Freshwater species live in ponds, lakes, rivers and estuaries. Most New Zealand freshwater fish, eels and salmon for example, have a marine stage in their life cycle. The inanga spawns in estuaries, and, after spending some months at sea, the tiny juveniles re-enter rivers and streams to grow to adulthood. Many of them don't make it, ending their journey in the waiting nets - at this stage of their lives, we know them as whitebait.

Marine species can be categorised according to whether they live in shallow, coastal or oceanic waters, and whether they live in the surface to midwater zone (pelagic) or are bottom-dwelling fish (demersal).

Age
Some fish species are very short-lived and grow quickly. Others are extremely long-lived, enjoying a longer lifespan than we do. Among the shortest-lived species are whitebait, which live only a maximum of three or four years, including their time as adults in fresh water. Several other marine species only live up to about five years, for example, anchovies, pilchards, sprats and flounders. Red cod and hoki also breed and grow quickly.

Many species live 10 or 15 years, but a number of very important fish species live to a remarkable age. Tarakihi grow to 20 or 30 years, trevally to 30 or 40 years, and snapper to over 60 years. These "middle order" species could be likened to animals like elephants or big cats, in terms of life expectancy.

The "tuatara" of the sea is the orange roughy, which is believed to live over 100 years.

Like people, the growth rates of some of the longer-lived species tend to flatten out after the first 10 or 15 years of their lives. In the case of snapper, the fish begin to breed less productively as they get past "middle age". By world standards, a high proportion of New Zealand fish species are long-lived.

top

Fisheries

Inshore fisheries Deep water fisheries Pelagic fisheries

The depth distribution of New Zealand's main marine fish species. Reproduced with kind permissions of Larry Paul, NIWA

Inshore fisheries
Traditional inshore fisheries are based on about 30 species. Their habitat extends from the shore out to depths of about 200 metres, at the edge of the continental shelf. Inshore species include flounder, sole, kahawai, snapper, john dory, groper, bluenose, tarakihi, red cod, blue cod, monkfish, kingfish, blue mackerel and trevally.

Deep water fisheries
The main concentrations of deep water species in New Zealand's 200-mile Exclusive Economic Zone (EEZ) are between about 40-55¼ S - that is a latitude running from about Taranaki down to south of Campbell Island. Deep water fish are harvested at depths ranging from 200-1500 metres.

Fishing in these seas, at these depths and in the winter months is very difficult; it wasn't until the early 1970s that many of these concentrations were found and harvesting techniques developed. Species in this zone include hoki, hake, ling, southern blue whiting, cardinal fish, warehou, orange roughy and the oreos. Among these are some of New Zealand's most important commercial fish species.

Black Oreo

top

Rock lobsters are undoubtedly our most important shellfish species and are widely distributed around New Zealand. Squid - strictly a mollusc rather than a fish - are also an important part of the commercial catch. They are found around both the main islands of New Zealand and to the south.

Rock Lobster

Other significant "wild" shellfish species include paua, scallops, oysters and scampi. Species such as surf clams - this name encompasses several species which live in the sand in the surf zone and in deeper waters - may have commercial potential.

Aquaculture
Farming of fish and shellfish is becoming well established around New Zealand. The main species are greenshell mussels and Pacific oysters. Salmon are also farmed, either in cages or through "ocean ranching".

There is potential for farming other species such as paua, rock lobster and kingfish.

Yellowtailed Kingfish

For more information click on any link below.