How Microalgae Are Used to Feed Marine Fish Larvae

Marine fish larvae are small, fragile and honest about their requirements. Almost none will eat a pellet on day one. Commercial larviculture therefore runs on live feeds — and live feeds run on microalgae. Understanding that chain, algae to zooplankton to larva, is the difference between a tank that survives and a tank that thrives.

The green water technique

In green water rearing, live microalgae are dosed into larval tanks as a light suspension. The algae are not mainly there to be eaten — though some larvae graze them. They shade harsh light, slow the degradation of zooplankton's nutritional value inside the tank, help dampen bacterial blooms and improve the visual contrast that striking larvae rely on. Small, robust species dominate the practice: Nannochloropsis for hardiness and EPA, Tetraselmis for size and reported antibacterial activity, Isochrysis where DHA matters most.

The live-feed chain

Most marine fish larvae are sized for zooplankton, not algae. Hatcheries therefore culture rotifers (historically Brachionus) as the first food, then Artemia nauplii, then weaning diets. Each zooplankton stage is itself fed microalgae or enriched with emulsions before it reaches the larvae, because zooplankton are nutritionally only as good as their last meal. Essential long-chain fatty acids — EPA and DHA — pass from algae through zooplankton to fish. That is the quiet reason a hatchery's algae room is as important as its broodstock room. For the fuller picture see how phytoplankton supports aquaculture food webs.

Where copepods fit

Rotifers and Artemia are convenient, but copepods are what many larvae evolved to eat: better size spectra, better swimming behaviour, and better nutrition without artificial enrichment. Copepod-based first-feeding protocols are increasingly common in ornamental and high-value marine aquaculture. Copepods need their own reliable algae ration, which is why we keep separate guides to feeding copepods and to choosing among the best microalgae for copepod culture.

What this means in practice

If you rear marine larvae, your real crop is algae: enough volume, freshness and the right species mix to feed rotifers, enrich Artemia, green the tanks and feed copepods. Densities and schedules differ sharply between species and systems — published hatchery manuals for your target species are the reference for numbers, not any general article, including this one.