Hatchery Production

Because the pipeline is purely multiplicative (fingerlings = eggs x fertilization rate x hatch rate x fry survival), scaling any one rate by a relative factor scales the final fingerling count by essentially that same factor — raising fertilization rate from 85% to 93.5% (a 10% relative increase) produces almost precisely 10% more fingerlings, because none of the other rates depend on fertilization rate's specific value. That's different from a percentage-POINT change, like 85% to 95%, where the proportional effect depends on which rate you're starting from — see the next question.

No. Overall survival rate is the product of fertilization rate, hatch rate, and fry survival rate alone — it describes what fraction of eggs make it through the pipeline, independent of how many eggs you started with. Doubling eggs spawned doubles the fingerling count and the loss figures at each stage proportionally, but the survival percentage itself stays exactly the same.

It's the inverse of your overall survival rate, and it answers a planning question directly: how many eggs you need to collect from spawning to reliably produce one fingerling. If your overall survival is 50%, you need roughly 2 eggs per fingerling; if survival drops to 25%, that doubles to about 4 eggs per fingerling, which is useful for sizing a broodstock program against a stocking target.

Because the three rates compound multiplicatively, an equal percentage-POINT improvement produces the biggest proportional gain in final output at whichever rate currently sits lowest — a 10-point gain is a much bigger relative move at a 60% rate than at a 90% rate. In practice, that stage is also usually where the cheapest operational fixes (broodstock condition, water quality, tank density) are available, since a rate that's fallen well below industry benchmarks for your species typically has an identifiable, fixable cause.