Reproductive biology and spawning substrate preferences of European Perch (Perca fluviatilis) from two New Zealand lakes

Abstract

European perch (Perca fluviatilis) has dominated freshwater systems in New Zealand since its introduction in 1868. This introduced species has established itself by outcompeting native species and altering the physicochemical properties of habitats. Eradication and control efforts in New Zealand seldom focus on initiating management at spawning, with little attention to their reproductive biology and plasticity. Despite many studies across the world focusing on these aspects, most are in the context of population protection within their native territories or in fisheries. Lake Rototoa and the Hamilton Lake (also known as Lake Rotoroa) are two lakes within the North Island of New Zealand that vary considerably in size and quality, and host populations of European perch that have dominated both systems. Sampling from both lakes occurred over a 12-month period, where measurements of body size, gonad development, fecundity and condition were collected to provide insight into each population’s health and reproductive biology. An artificial spawning substrate experiment over six weeks consisted of three different substrates at five sites in both lakes and in laboratory tanks to investigate the potential for spawning substrate preferences. A total of 159 perch were caught and dissected from the Hamilton Lake, and 126 were caught and dissected from Lake Rototoa. Spawning appeared to be asynchronous at Lake Rototoa from condition and GSI results, and synchronous at the Hamilton Lake. Size and condition indices were higher at the Hamilton Lake and displayed some seasonal patterns. Fecundity at the Hamilton Lake ranged from 71,202 to 80,400.96 compared to 40,844 to 73,232.21 eggs per female at Lake Rototoa during the spawning season. Oocyte diameters were slightly larger at the Hamilton Lake, with a range of 0.836 mm and 2.019 mm compared to 0.839 mm and 1.886 mm at Lake Rototoa. Perch did not use any artificial spawning substrates at all three sites. Results suggested a more stunted population at Lake Rototoa, likely due to different water qualities and resource availability. These results provide a solid foundation for control methods targeting spawning strategies in European perch. However, improved techniques for artificial spawning substrates are necessary, particularly focusing on the location and timing of where and when they are deployed.