How much phytoplankton do copepods need?

Copepods feed continuously, so most culturists feed small amounts often rather than one large dose. The right density depends on the copepod species, life stage, volume and harvest schedule — start low, watch the water clear, and adjust. Published hatchery manuals give starting densities for the species you keep, and they vary widely between species.

Can copepods starve in green water?

Yes. Green coloration is not nutrition. A diet of the wrong cell size, senescent algae, or a mono-diet missing essential fatty acids can leave copepods food-limited even when the tank looks green. Egg production and nauplii counts are better signals than colour.

Should I feed one algae species or a mix?

Mixed diets generally support better reproduction than any single species, because algae differ in size, digestibility and fatty-acid profile. Many aquaculturists pair a small flagellate such as Isochrysis with a larger green cell such as Tetraselmis. Treat that as a starting point and validate with your own animals.

How to Feed Copepods With Phytoplankton

Copepods are the working animals of marine larviculture. They are what many fish and shellfish larvae eat best, and what they eat best is live microalgae. Feeding copepods well is therefore a two-link problem: you grow an algae culture to grow a crustacean culture to grow the animal you actually care about. This article is about the first two links — what phytoplankton does for copepods and how to deliver it.

Why live microalgae, not dry feed

Most planktonic copepods graze particles by size and motion. Live microalgal cells stay suspended, do not decay into ammonia the way uneaten dry feed does, and arrive wrapped in the lipids and sterols copepods cannot synthesise well themselves. Copepod egg production tracks dietary quality closely — a well-fed female is an egg factory, a poorly fed one simply stops. That sensitivity is why cultured algae, harvested young and fed fresh, outperform leftovers.

The factors that actually matter

Cell size and shape. A copepod can only ingest what fits its mouthparts and what its feeding currents can capture. Small flagellates in the low single-digit micrometres suit nauplii; larger cells suit adults. Match the algae to the life stage, not the other way round.
Density. Too little and the copepods spend energy searching; too much and you risk water-quality problems and wasted algae. Feed to a density the culture clears visibly within hours, then adjust.
Nutritional profile. Long-chain fatty acids such as EPA and DHA, and sterols, drive reproduction. Flagellates such as Isochrysis and Pavlova are valued largely for these lipids.
Freshness. Cells harvested near peak density and fed the same day carry more of what copepods need than cultures held for days — which also carry heavier bacterial loads.

Why species respond differently

There is no universal copepod diet. Acartia species, harpacticoid Tisbe, and the Apocyclops and Pseudodiaptomus species common in ornamental aquaculture differ in what they capture, digest and invest in eggs. A mono-diet that sustains one species can quietly starve another. The practical approach is a mixed diet — typically one small flagellate plus one larger green cell — plus observation: egg output, nauplii counts and stable culture colour tell you whether the ration works.

Delivery practices that help

Feed small amounts frequently rather than a weekly dump. Strain or screen the algae if your culture method carries debris. Keep the schedule consistent — copepod cultures crash more often from dietary gaps than from single catastrophes. And culture your own algae rather than buying by the bottle: once you can maintain two reliable microalgae cultures, feeding copepods becomes a scheduling problem, not a procurement one.