Larviculture and Live Feeds in Aquaculture Hatcheries: A Guide

How hatcheries rear fish larvae: why larvae are fragile, the live feeds used (microalgae, rotifers, Artemia), the green-water technique, HUFA enrichment, the first-feeding sequence, and weaning.

Overview

Larviculture is the rearing of fish and shellfish through the larval stage, the most delicate and often the most failure-prone phase of a hatchery. Newly hatched larvae are tiny, have a small mouth gape and an undeveloped digestive system, and cannot eat or digest ordinary formulated feed at first. Live feeds, organisms cultured and fed live, bridge this gap until the larvae are large and developed enough to accept manufactured diets.

Why larvae need live feeds

At first feeding, many marine larvae can only capture and digest small, moving prey. Live organisms are the right size for a small mouth, move in a way that triggers feeding, and carry enzymes and nutrients that help the immature larval gut. For these reasons most marine fish hatcheries depend on a planned sequence of live feeds before any dry diet is introduced.

The main live feeds

FAO identifies three groups of live diets widely used in marine larviculture, distinguished largely by size.

• Microalgae (phytoplankton), about 2 to 20 micrometres, cultured species such as Nannochloropsis, Chlorella, Isochrysis and Tetraselmis.
• Rotifers, the species Brachionus plicatilis, roughly 50 to 200 micrometres, the usual first prey for many small larvae.
• Artemia (brine shrimp), about 200 to 500 micrometres as newly hatched nauplii, fed after the rotifer stage.

The green-water technique

Many hatcheries add microalgae directly to the larval rearing tank, giving the water a green tint. FAO notes that this green-water technique stabilizes water quality in static systems, serves as a food source, improves feeding by increasing visual contrast and light dispersion, and provides microbial control. The algae also help sustain the nutritional quality of rotifers and Artemia held in the tank.

Artemia and enrichment

A key advantage of Artemia is that it is sold as dormant cysts that store for long periods and hatch on demand; the cysts hatch within roughly a day, and the newly hatched nauplii are less than about 0.4 mm long. However, rotifers and Artemia are not naturally rich in the highly unsaturated fatty acids (HUFA), especially DHA, that marine larvae require. Before being fed to larvae they are therefore enriched (bio-encapsulated) by feeding them DHA- and EPA-rich products for a period of hours, which raises their food value.

First-feeding sequence and weaning

Live feeds are offered in order of increasing size as the larvae grow. Small larvae typically start on enriched rotifers, move on to Artemia nauplii after the first days, and are then gradually weaned onto formulated microdiets as their mouths and guts develop. The timing depends on species and larval size, and overlapping the feeds during transition helps the larvae accept the dry diet. Careful water quality, gentle aeration and steady feeding through these stages are decisive for survival.