Species profiles
Feeding A diurnal, shoaling visual predator: strike efficiency peaks at intermediate light — not deep shade and not harsh glare (Helfman 1981; Diehl 1988). The profile centres the main feeding window around midday and late afternoon (Jamet & Lair 1991; Eriksson 1978).
Temperature Perch tolerate warmth better than most other profiled species: aquaculture work reports growth optima near 23 °C, while coastal wild recruitment is often strongest around 16–22 °C at the surface. Above ~28 °C fish retreat to cooler layers and feeding shuts down.
Reproduction Spring spawning in the shallows: females deposit adhesive egg ribbons on submerged plants or rocks; males follow and fertilise. Eggs are tough, but cannibalism among larvae can be severe in dense populations.
Feeding Pike are textbook ambush predators: they use cover and the contrast between prey silhouette and light. Hard sun reduces success; solid overcast softens activity slightly. Light-to-moderate wind and chop disorient prey and cut surface glare — both favour pike (Lehtonen & Niemelä 1986; Casselman & Lewis 1996).
Temperature Literature growth optima near 21–23 °C; feeding tapers when warm surface water exceeds ~25 °C. In winter and spring, feeding can stay steady from roughly 10 °C upward (telemetry studies).
Reproduction Spring flooded meadows and weedy shallows: females scatter batches of sticky eggs; males fertilise externally. Spawning sites are temperature- and oxygen-sensitive; vegetation gives fry cover.
Feeding Zander are low-light specialists: large pupils and a tapetum lucidum yield at least twice pike retinal sensitivity under the same conditions (Horppila et al. 2018). Strikes concentrate below ~1 lux (Bergman 1991). The profile therefore favours cloudy skies and a strong moon term — moonlight extends the feeding window.
Behaviour Diel rhythm leans to evening, night, and around midnight: fish move up in the water column at dusk to hunt smelt, perch, and similar prey (Schulze et al. 2006). Calm water supports tight shoals; rough surface chop breaks them up (Pekcan-Hekim et al. 2010).
Reproduction Spawning often on sand or gravel bars and basin margins in spring; males guard eggs. Population density and lake trophic state strongly affect larval survival.
Feeding Feeding shifts with life stage. Upriver adults stress above ~20 °C; migration can stall (Solomon & Sambrook 2004; DFO). The profile stresses cool water (lower optimum than brown trout) and reduced surface light (Karppinen et al. 2002; Kadri et al. 1991).
Behaviour Dawn-skewed activity versus a secondary dusk peak. In coastal angling, light chop can bunch baitfish and mask lure entry (Lacroix & McCurdy 1996).
Reproduction Autumn redds in gravelly riverbeds: females excavate a pit, eggs are buried in gravel. Sea-run fish home to natal streams; landlocked strains adapt to lakes.
Feeding Burbot are benthic and night-active: in summer, locomotor activity is roughly 180° out of phase with daylight; under polar-night winter, daytime activity can increase (Müller 1973). Shallow nocturnal excursions cluster at twilight (Harrison et al. 2013).
Temperature Bioenergetic growth stalls above ~18 °C; thermal preferendum near 13 °C. Burbot feed and move in the cold — winter spawning under ice at 0–4 °C (Hofmann & Fischer 2002; Cott et al. 2013).
Reproduction Mid-winter spawning under ice; eggs develop slowly in cold, oxygen-rich water. Young stages are small benthic predators.
Feeding Whitefish are planktivores and daytime visual feeders: stomach fullness peaks by day, partly under clear or partly cloudy skies; solid overcast can depress activity (Mookerji et al. 1998; Eckmann et al. 2002). They track diel zooplankton migrations (Mehner et al. 2005).
Temperature Cold-stenothermal: sustained feeding commonly 7–14 °C; above ~18 °C fish drop deep (Wanzenböck et al. 2002). A stable thermocline matters — predictable shoal depth for pelagic feeding bouts.
Reproduction Spawning on bottom or in deep basins depending on form; eggs need cold, oxygenated water. Finland hosts multiple morphs with different niches.
Feeding Baltic herring are obligate schoolers: feeding peaks when surface irradiance is low (dusk, overcast) as zooplankton move up and herring follow (Cardinale et al. 2003). Moonlight extends near-surface feeding but less than for zander or burbot.
Temperature Recruitment and feeding align with roughly 4–14 °C surface water; feeding stalls below ~2 °C; above ~16 °C stocks often shift farther offshore (Rajasilta 1992; Cardinale et al. 2009).
Reproduction Spring demersal spawning; timing and egg mass depend on food, condition, and environmental noise — year-classes are highly variable in the Baltic.
Feeding Brown trout are a cold-water salmonid: thermal preferendum near 12 °C, growth strongest 13–17 °C, feeding fades above ~19 °C (Elliott & Elliott 2010). Feeding is strongly dawn- and dusk-peaked with a deep midday lull (Ovidio et al. 1998; Bunnell et al. 2017). Light rain boosts invertebrate drift — the profile encodes a "light rain" window (Steingrímsson & Gíslason 2002; Bachman 1984).
Reproduction Autumn spawning on gravel in flowing water; lacustrine strains may use littoral zones. Sea-run ("sea trout") migrations and spawning track flow and temperature regimes.