Freshwater eels have an unusual life cycle which sees them travelling between the ocean, estuaries and freshwaters.
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Tuna - identification
There are several ways to tell the three New Zealand eel species apart. -
Tuna - life cycle and leptocephalii
Freshwater eels have an unusual life cycle which sees them travelling between the ocean, estuaries and freshwaters. -
Tuna - glass eels
Glass eels (about 5.5 to 7.0 cm) arrive in fresh water during spring, especially during September and October, although they may be present from July to December. -
Tuna - elvers and recruitment
Once in freshwater, glass eels develop into darker pigmented juvenile eels known as elvers. -
Tuna - habitat
Tuna are found in all sorts of habitats (places), including coastal estuaries, lakes, wetlands, rivers, mountain streams and even alpine tarns. -
Tuna - diet
Longfin eels are the largest and longest-lived fish in New Zealand's freshwaters, and where they are present they are the top predator. -
Tuna - growth
New Zealand longfins are one of the largest eel species in the world, and have been recorded at sizes of almost 2 m in length and more than 50 kg in weight. -
Tuna - maturation and identifying sex
The sex of tuna is not determined genetically, as in some other organisms. -
Tuna - age and methods of ageing
Knowing the age (i.e. proportion of young vs. old) of eels in an eel population provides an understanding of how fast they grow and may give an indication of the pressures faced by tuna in a particular environment or habitat. -
Tuna - tuna heke (downstream migrants)
Every year, a proportion of eels mature and migrate to sea to spawn. Once eels become migrants (also known as tuna heke or tuna whakaheke) they stop feeding, and progressively develop the external features that clearly distinguish them from 'feeders'. -
Tuna - spawning grounds
All species of freshwater tuna spawn at sea, although the spawning grounds of only four species are known with certainty worldwide.