Fry and Larval Tanks

Fry and larval tanks are used after hatching and yolk sac absorption, when young fish begin exogenous feeding and become fully dependent on environmental conditions and nutrition. This stage is often one of the most sensitive in aquaculture, as small changes in water quality, feeding, light, or stocking density can strongly affect survival, growth, and later production performance.

Larval tanks are typically shallow and designed with gentle hydraulics to minimize stress and ensure that weak-swimming larvae can easily access feed. Water flow must provide sufficient oxygen and waste removal without creating excessive currents that force larvae to expend energy or become trapped against screens.

First feeding

The transition to first feeding is a critical developmental milestone. Larvae must locate and consume feed before yolk reserves are exhausted. In many marine species, live feeds such as rotifers and Artemia are used during the earliest stages before gradual introduction of formulated feeds. Freshwater species such as salmonids typically transition directly to commercial starter diets after yolk sac absorption.

Light, density and grading

Light intensity and photoperiod are important design and operational considerations. Many species require specific light regimes to locate feed, regulate behaviour, and support growth. Excessive light can increase stress, while insufficient illumination may reduce feeding efficiency. Hatcheries often use programmable lighting systems. Stocking density must be carefully controlled. High densities can improve space utilization but may increase competition, stress, oxygen consumption, disease transmission, and size variation. Frequent grading is often required to reduce cannibalism in species such as perch, pike-perch, barramundi, and many marine fish.

Modern fry-rearing systems increasingly incorporate automated feeding, oxygen control, image-based monitoring, and environmental sensors for more consistent results. See monitoring systems, dissolved oxygen and feed.

Typical species

• Atlantic salmon, rainbow trout, Arctic char
• Tilapia, common carp
• Pike-perch, European perch
• Sea bass, sea bream, Atlantic cod, halibut
• Shrimp (e.g. Litopenaeus vannamei) — see differences vs fish below

Typical design parameters (fish)

Teaching ranges. Fry and larvae are sensitive — aim toward the safer side of the ranges. Not a protocol.

Simple sizing (fish)

Volume ≈ number of fry / target density (fish/m³), or volume ≈ biomass / target biomass density (kg/m³). Example: 100,000 salmon fry at 10,000 fry/m³ → 10 m³. Alternatively 200 kg fry at 20 kg/m³ → 10 m³.

Important operational factors

• First-feeding success often determines overall hatchery performance.
• Oxygen demand increases rapidly as feeding begins.
• Uneaten feed must be removed to prevent water quality deterioration.
• Frequent grading reduces size variation and cannibalism.
• Stable temperature and photoperiod improve growth uniformity.
• Backup oxygen systems are strongly recommended — young fish are sensitive.

How shrimp tanks differ from fish tanks

Fish use the water column and swim. Shrimp are largely bottom-dwelling: they walk, graze, hide and moult. Design therefore differs clearly even though both are reared in “tanks”.

Area vs volume

Fish tanks are usually sized as density in kg/m³ (or fish/m³). For shrimp — especially larger juveniles and grow-out — the limit is often animals/m² or kg/m² because animals occupy the bottom. A shrimp tank may therefore be shallower and wider than a fish tank holding similar biomass. Many systems add extra surface: meshes, sheets, net curtains, artificial seaweed or biofloc structures — several times the floor area. For fish, extra surface is rarely relevant except as biofilter media.

Hydraulics, bottom and moulting

Fish tanks may use circular flow for swimming stimulus and self-cleaning. Shrimp tanks need gentler hydraulics: avoid strong currents, protect moulting animals, avoid feed in corners. Flow is mainly for oxygen and solids. Faeces and feed sink quickly; bottom deposits favour Vibrio. Hence: central drains, sloped floors, bottom flushing, frequent sludge removal. During moulting shrimp are vulnerable to cannibalism, mechanical damage and water-quality swings — habitat, stable salinity, alkalinity and calcium/magnesium become critical (often monitored as carefully as DO).

Density, feed and biofloc

Intensive shrimp culture can reach animal densities impossible for most fish. Orientation: extensive ponds a few shrimp/m²; semi-intensive often tens to ~150/m²; intensive lined ponds and indoor RAS much higher (hundreds–thousands/m² depending on stage). Fish are more often limited earlier by oxygen and swimming behaviour. Shrimp feed mainly on the bottom, more slowly and continuously — multiple daily feeds, feed trays, automatics, acoustic sensors and cameras are common. Biofloc (BFT) is widespread in shrimp: microbial aggregates consume ammonia and are grazed by shrimp; FCR and water exchange can improve. Fish RAS often aims to remove suspended solids, whereas biofloc intentionally maintains them.

Simple shrimp nursery sizing: area (m²) ≈ number of shrimp / target density (shrimp/m²). Example: 100,000 nursery shrimp at 500/m² → 200 m². Fish systems are normally sized primarily from tank volume and biomass density instead.

In short: fish tanks are generally designed around water volume and swimming behaviour; shrimp tanks often around bottom area, surface area, feeding behaviour and moulting biology. That is why modern indoor shrimp farms frequently use shallow raceways, lined ponds, stacked nursery tanks and large amounts of artificial substrate, while salmon, trout, char, sea bass and tilapia are more commonly reared in circular tanks, raceways or cages designed around volume and hydraulic performance.