Fish Age from Length Calculator
Estimate the age of a fish from its length.
Uses species-specific growth models for trout, bass, walleye, and common freshwater species.
Fish age can be estimated from length using species-specific von Bertalanffy growth models. This is an approximation — actual age varies significantly between populations, water temperatures, food availability, and geographic location.
Von Bertalanffy growth model: L(t) = L∞ × (1 − e^(−K × (t − t₀)))
Where:
- L(t) = length at age t
- L∞ = asymptotic maximum length
- K = growth coefficient
- t₀ = theoretical age at length zero
Rearranged to estimate age from length: t = t₀ − (1/K) × ln(1 − L/L∞)
Typical maximum lengths and growth rates:
| Species | Max Length | Growth Pattern |
|---|---|---|
| Rainbow Trout | 70–100 cm | 10–15 cm/year early |
| Brown Trout | 80–100 cm | 8–12 cm/year early |
| Largemouth Bass | 60–80 cm | 8–15 cm/year |
| Walleye | 80–100 cm | 10–15 cm/year |
| Northern Pike | 100–150 cm | 15–25 cm/year |
| Atlantic Salmon | 100–120 cm | Variable |
Why age matters for conservation: Older, larger fish are disproportionately important for reproduction. A 50 cm female trout may produce 3–5x more eggs than a 30 cm female. Catch-and-release of trophy fish preserves the breeding population and future fishing quality.