Best Microalgae for Copepod Culture: an Honest Comparison

Ask ten copepod culturists for the best algae and you will get eleven answers, most of them correct for their own animals. The honest framing: there is no universally best species, only better or worse matches between one copepod's mouthparts and metabolism and one alga's size and biochemistry. Here is how the usual candidates compare.

The candidates, at a glance

• Isochrysis / Tisochrysis (T-Iso) — a small (roughly 4–6 µm) haptophyte flagellate, prized for DHA and ease of culture. The default first flagellate in many marine live-feed programs.
• Pavlova — another small haptophyte, with a strong EPA and DHA profile and good tolerance of varying salinity. Pairs naturally with T-Iso.
• Nannochloropsis — tiny (2–3 µm), thick-walled, extremely hardy, EPA-rich. A green water and rotifer workhorse; for copepods it is usually a component rather than the whole diet.
• Tetraselmis — a larger (roughly 8–15 µm) motile green alga with starch and lipid reserves. Suits adult copepods of many species and adds dietary breadth.
• Chaetoceros — a chain-forming diatom used widely in bivalve and shrimp hatcheries; some copepods graze it well, and it brings a diatom's sterols and pigments to the table.
• Rhodomonas — a cryptophyte flagellate popular with hobbyist and commercial copepod growers for its high nutritional value; notoriously less forgiving to culture than the list above.

How to choose without guessing

Three filters narrow the field. First, size match: nauplii need cells in the low micrometre range; adults can take larger cells and even some chains. Second, digestibility: thick-walled or mucilage-producing cells defeat some grazers entirely. Third, nutrition: reproduction runs on long-chain fatty acids and sterols, which is why the small flagellates carry so much reputation per micrometre.

In practice, most copepod programs that work run two species minimum — for example T-Iso plus Tetraselmis, or Pavlova plus Nannochloropsis — because a mix covers size ranges and hedges against one culture crashing. Start from a published recipe for your copepod, then let egg output and nauplii counts override theory. And keep a written record: 'what we fed' versus 'what the culture did' is the only dataset that settles the question for your animals.

The metabolic point people miss

Feeding copepods is really feeding the next link's chemistry. Marine larvae need EPA and DHA they cannot make efficiently themselves; copepods assemble them from their own diet; their diet is your algae culture. Choosing algae for copepods is choosing the fatty-acid signature your fish or shellfish will inherit. That is why we treat the algae room as part of the larval system, not a supply closet — and why our species guides link both directions, from algae to the animals they feed.