What does it look like?
Perch are olive green-grey, with six or more dark vertical bands across their sides. The pelvic and anal fins and lower half of the tail are bright red-orange. Adults reported at around 400-450mm long, 1-2kg overseas, but most fish in the Auckland region are less than 1kg, less than 400mm. Maximum recorded age in New Zealand is eight years, but they are known to live to 20 plus years overseas.
Perch shoal as young, and are more solitary as adults. Larvae eat free swimming zooplankton; larger juveniles eat benthic macroinvertebrates. Adults mainly eat other fish (including cannibalising juvenile perch). Predominantly active during the day, perch is a warm-water species, and becomes less active during winter. Tolerates a wide temperature range. Prefers still or slow moving freshwater bodies. Adults tend to utilise lake margins need emergent vegetation. Juveniles also use open waters.
Why is it a problem?
Perch prey on zooplankton, macroinvertebrates and fish, and have the potential to significantly alter native freshwater communities, through predation and competition with native fish species. They show habitat and behavioural flexibility and fill a niche not represented within native freshwater fauna. Perch can dominate fish fauna of freshwater bodies and are invasive overseas.
This species, as with most pests, has high fecundity potential. Most males spawn in the first year, most females not til the second year. They spawn in spring in the northern hemisphere, but there is some evidence that they may have an extended spawning season in Auckland due to the warm climate. Eggs are laid in long strings of between 5000-80,000 eggs. No parental care is provided, and young fish grow rapidly in the first year. Recruitment varies between years in response to environmental variables, resulting in strong year classes being apparent. Cannibalism can regulate recruitment, structuring the population towards low overall abundance and dominance by a few large individuals.
Please contact the Northland Regional Council if you think you have seen this pest.