How Fisho's Bite Times Work

The data behind Fisho's solunar predictions, activity ratings, tide charts, species calculators, and legal size data — explained plainly.

What is solunar theory?

Solunar theory holds that fish and other animals are more active during specific time windows determined by the positions of the moon and sun relative to a given location on Earth. The theory was developed and published by American naturalist John Alden Knight in 1926, who observed that fish feeding behaviour correlated with lunar and solar transit times.

Decades of angler observation have validated the core finding: fish are statistically more likely to feed during the two daily Major periods (when the moon is directly overhead or underfoot) and the two Minor periods (at moonrise and moonset). This holds across species and across freshwater and saltwater environments.

How Fisho calculates solunar periods

Fisho calculates solunar periods entirely server-side using sun and moon ephemeris calculations for your exact latitude and longitude coordinates. There is no third-party solunar API — the mathematics are performed in-memory on each request using published astronomical algorithms.

This means Fisho can provide bite times for any point in New Zealand (or globally) to any precision — not just a set of pre-defined locations. When you drag the map pin in the location picker, you are getting bite times calculated for that exact point.

Each day produces four solunar periods:

• Major periods (×2 per day): Occur when the moon transits overhead (lunar culmination) or underfoot (nadir). Duration approximately 2 hours each. These are the strongest feeding windows.
• Minor periods (×2 per day): Occur at moonrise and moonset. Duration approximately 1 hour each. Produce moderate feeding activity, particularly on high-rated days.

What the activity rating means

The daily activity rating (shown as fish icons, 1–5) is a composite score that reflects how strongly lunar and solar forces are aligned on a given day. The primary driver is moon phase:

• Excellent (5/5): New or full moon — maximum gravitational influence, strongest solunar periods.
• Very Good (4/5): Approaching or just past new/full moon.
• Good (3/5): First or last quarter moon phases.
• Fair (2/5): Waxing or waning crescent/gibbous phases.
• Slow (1/5): Minimal lunar influence — solunar periods are present but less pronounced.

Excellent days occur approximately four times per month (around each new and full moon). The monthly calendar on the Bite Times page displays the activity rating colour-coded for every day, allowing you to plan sessions weeks in advance.

Tide data — NIWA

Fisho's tide data is sourced directly from the National Institute of Water and Atmospheric Research (NIWA) Tidal API. Tide predictions for 15 New Zealand gauge locations are pre-ingested daily via a background job (running at 1am NZT), storing 60 days of predictions in Fisho's database for fast retrieval.

The 15 NIWA tide gauge locations currently supported are:

• Auckland (Waitemata Harbour), Tauranga, Whitianga, Gisborne, Napier, Wellington, Nelson, Westport, Lyttelton, Timaru, Dunedin, Bluff, Picton, Whangarei, Taupo Bay.

The tide chart on the Bite Times page uses cosine interpolation between prediction points to produce a smooth curve, rendered in-browser using Chart.js.

Species weight constants

The Fish Weight Calculator estimates the weight of a fish from a measured length using the length-weight formula: W = a × L^b, where a and b are species-specific constants.

The constants used for each New Zealand species are sourced from peer-reviewed publications hosted by NIWA and FishBase (fishbase.org), the global reference database for fish biology. The seven species currently covered:

Species	Scientific name	Source
Snapper	Pagrus auratus	NIWA / FishBase
Kingfish (Yellowtail)	Seriola lalandi	FishBase
Kahawai	Arripis trutta	NIWA
Blue Cod	Parapercis colias	NIWA
John Dory	Zeus faber	FishBase
Tarakihi	Nemadactylus macropterus	NIWA
Striped Marlin	Kajikia audax	IGFA / FishBase

Legal size data

Minimum legal size and daily bag limit data displayed in the Fish Weight Calculator is sourced from Fisheries New Zealand (MPI) — the New Zealand Ministry for Primary Industries. Regulations are reviewed against MPI published tables and updated when rule changes are announced. Always confirm current regulations at mpi.govt.nz before fishing.