Egg incubators are used to provide stable and controlled conditions during the sensitive early life stages of fish. Their purpose is to maximize hatching success, reduce disease risk, and ensure uniform development from fertilized eggs to first-feeding larvae or fry.
Successful incubation depends on maintaining the correct water temperature, dissolved oxygen level, flow rate, and water quality for the species being cultured. Most incubators are kept in low light or darkness, as fish eggs naturally develop in shaded environments and excessive light can increase stress and reduce hatch quality in some species.
Flow and water quality
Water flow serves several functions. It delivers oxygen, removes carbon dioxide and metabolic waste products, prevents stagnant zones, and helps keep eggs clean. Flow must be strong enough to maintain good water quality but gentle enough to avoid damaging delicate eggs.
Dead or unfertilized eggs should be removed regularly. These eggs are often quickly colonized by fungi such as Saprolegnia, which can spread to healthy eggs and cause significant losses. Modern hatcheries may use manual inspection, siphoning, automated sorting systems, or image-based monitoring to identify and remove non-viable eggs. See also egg disinfection and biosecurity.
Common incubator designs
Different incubator designs are used depending on the species:
- Vertical tray incubators - common for salmonids (Atlantic salmon, rainbow trout, Arctic char, brown trout). See Heath trays.
- Upwelling jars (McDonald jars) - widely used for species with small pelagic eggs or eggs that benefit from gentle suspension in the water column.
- Heath tray incubators - simple, proven and common in many hatcheries; own section under hatchery.
- Specialized systems - marine fish, sturgeon, carp, tilapia, shrimp and others with their own flow, salinity and density needs.
Temperature and development
Temperature has a major influence on development speed. Warmer water generally accelerates embryonic development, while colder water slows it down. However, temperatures outside the species-specific optimum range may increase deformities, mortality, or poor larval quality. For this reason, many hatcheries use temperature-controlled water systems to maintain precise conditions throughout incubation. See temperature and dissolved oxygen.
Monitoring in modern hatcheries
Modern commercial hatcheries increasingly monitor egg survival, hatch rate, temperature, dissolved oxygen, pH, flow rate, and developmental progress using digital sensors and automated alarm systems. Early detection of problems can significantly improve productivity and biosecurity. Hatcheries are also extremely sensitive to power loss - see backup power systems.
Good egg incubation practices often determine the performance of the entire production cycle. High-quality eggs, stable environmental conditions, careful handling, and effective disease prevention are among the most important factors for achieving strong fry and fingerlings.
Key parameters to monitor
- Water temperature
- Dissolved oxygen (DO)
- Water flow rate
- pH and alkalinity
- Ammonia and nitrite
- Egg mortality rate and hatch percentage
- Biosecurity and fungal growth
Typical species using hatchery incubators
- Atlantic salmon (Salmo salar)
- Rainbow trout (Oncorhynchus mykiss)
- Arctic char (Salvelinus alpinus)
- Brown trout (Salmo trutta)
- Sturgeon (Acipenser spp.)
- Common carp (Cyprinus carpio)
- Tilapia (Oreochromis spp.)
- Sea bass (Dicentrarchus labrax)
- Sea bream (Sparus aurata)
- Various shrimp and other marine fish species
Sizing (orientation)
Incubator sizing is usually based on annual fry production, egg-to-fry survival, and how long eggs stay in the incubator. A simple chain:
- Eggs per year: N_eggs = N_fry / S (S = survival as a decimal).
- Incubation time: days = degree-days (°D) / temperature (°C).
- Simultaneous inventory (steady year-round production): N_inv ≈ N_eggs × (days / 365).
- Volume: V = N_inv / (eggs per litre); design volume often 1.2–1.5 × V.
- Flow (salmonid rule of thumb): Q ≈ 0.02–0.05 L/min per 1000 eggs × N_inv.
Typical egg incubation characteristics by species
The table gives approximate orders of magnitude for egg size, packing density, degree-days to hatch and typical incubation temperature. Strain, broodstock status, salinity and hatchery practice cause large differences — use as orientation, not a protocol.
| Species | Egg Ø (mm) | Eggs/L (approx.) | °D to hatch | Temp (°C) |
|---|---|---|---|---|
| Atlantic salmon | 5.5–7.0 | 6 000–8 000 | 400–550 | 6–10 |
| Rainbow trout | 4.5–6.0 | 7 000–10 000 | 280–420 | 8–12 |
| Arctic char | 4.5–5.5 | 8 000–12 000 | 450–650 | 4–8 |
| Brown trout | 4.0–6.0 | 7 000–10 000 | 350–500 | 6–10 |
| Coho salmon | 5.0–6.5 | 6 000–9 000 | 450–550 | 6–10 |
| Chinook salmon | 6.0–8.0 | 5 000–7 000 | 500–700 | 5–10 |
| Sturgeon | 2.5–4.0 | 20 000–50 000 | 70–150 | 15–22 |
| Common carp | 1.2–1.8 | 100 000–200 000 | 60–90 | 20–28 |
| Grass carp | 1.5–2.0 | 80 000–150 000 | 40–80 | 22–30 |
| Tilapia | 2.0–3.0 | 30 000–80 000 | 70–120 | 26–30 |
| Pike-perch (zander) | 1.3–1.8 | 100 000–180 000 | 80–120 | 12–18 |
| European perch | 1.0–1.5 | 150 000–300 000 | 80–120 | 10–18 |
| Sea bass | 1.0–1.3 | 300 000–700 000 | 70–110 | 13–18 |
| Sea bream | 0.9–1.1 | 500 000–1 000 000 | 40–80 | 16–22 |
| Atlantic cod | 1.2–1.5 | 250 000–500 000 | 90–150 | 4–8 |
| Halibut | 3.0–4.0 | 20 000–60 000 | 250–500 | 5–8 |
| Whiteleg shrimp (L. vannamei) | — | millions of larvae / L-scale* | — | 28–31 |
| Giant river prawn (M. rosenbergii) | — | millions of larvae / L-scale* | — | 28–31 |
* Shrimp are often incubated/larval-reared at much higher density and in different units than salmonid eggs — do not compare directly with salmonid eggs/L. Teaching ranges; strain and hatchery practice govern.
Typical commercial scale
Orders of magnitude for hatchery batches. A “batch” can mean a hatch window or a production round — not a global standard.
| Species | Typical hatchery batch (orientation) |
|---|---|
| Arctic char | ~0.1–5 million eggs |
| Rainbow trout | ~0.5–20 million eggs |
| Atlantic salmon | ~1–50+ million eggs |
| Sturgeon | ~10,000–5 million eggs |
| Tilapia | ~10,000–500,000 eggs |
| Carp | ~100,000–50 million eggs |
| Sea bass | ~1–50+ million eggs |
| Sea bream | ~1–100+ million eggs |
| Shrimp | ~10–500 million larvae |
Scale varies enormously with company, market and species. Use as order-of-magnitude in early sizing.
The calculator below uses mid-range values from the table for common presets (salmon, trout, Arctic char, tilapia, carp). Adjust eggs/L, °D and temperature to your protocol.
Calculator: egg incubator sizing (orientation)
Incubator type
© 2026 DABCE AB
Example (worked illustration, Arctic char preset): 1,000,000 fry/year, 80% survival → 1,250,000 eggs/year. At 6 °C and 550 °D → about 92 days; simultaneous inventory ≈ 314,000 eggs; at 10,000 eggs/L ≈ 31 L; with 1.5× spare ≈ 47 L active incubation volume across trays or units. Try the same numbers in the calculator. Oxygen-based flow sizing (Q = M_O₂ / ΔDO) can become limiting near hatch — see dissolved oxygen.
Levelling biology over the year
The calculator above effectively assumes steady year-round production: eggs are incubated more or less continuously so inventory and tank capacity can be sized on “eggs at once”. In reality salmonids in general are driven by seasonal breeding cycles — rainbow trout, Atlantic salmon, Arctic char, brown trout and others — as long as the broodstock environment is not controlled with light and temperature. Wild stocks and farmed broodfish under natural light/temp spawn in a limited window. Without deliberate planning the hatchery gets a large egg pulse over a few weeks and then long periods with empty trays. That loads incubators, staff, fry tanks and later grow-out unevenly — and means the “tonnes per year” in a spreadsheet do not match the actual biology.
If you want to level the flow of fry and food fish over the year, there are essentially two strategic paths (often combined):
1. Freeze / bank eggs
Milt (sperm) from salmonids can be cryopreserved (frozen) with established technique and thawed when needed. Unfertilised eggs are far more sensitive: egg banking by deep-freezing ova is not standard to the same extent as for milt, although research and specialised methods continue. In practice, “freezing the biology” therefore often means: store frozen milt, and/or hold fertilised eggs in controlled, slow development (cold water, planned °D budget) so hatch is spread — more “tempered delay” than a freezer. Some hatcheries also buy eyed eggs from several suppliers or seasons to fill gaps. The same logic applies to rainbow trout, salmon and Arctic char: without light-/temperature-controlled broodstock (or bought eggs from several windows), egg supply clumps — planning egg supply and incubation temperature is then critical if you want to avoid a single annual peak.
- Advantages: partly decouples the broodstock week from when fry are needed; frozen milt gives breeding flexibility and backup.
- Limits: ova are harder to store long-term than milt; quality, logistics and rules around brood material; not a “freezer = level production” shortcut.
2. Manipulate broodstock cycles
The second path is to control when broodstock spawn. Salmonids — rainbow trout, Atlantic salmon, Arctic char and others — respond strongly to light (photoperiod) and temperature. Under natural light and seasonal temperature, spawning is therefore seasonal. With controlled light regimes — and often temperature — one can shift, compress or spread spawning: e.g. several brood groups out of phase, out-of-season eggs, or more than one spawn season per year in closed systems. That is a standard tool in many commercial salmonid hatcheries, not only for one species. In land-based farming (RAS/semi-flow) the reason is especially clear: you want to fill tanks evenly year-round to use CAPEX, labour and market capacity.
- Photoperiod: longer/shorter day length drives maturation and spawning in many salmonids — needs dark halls, timers and discipline.
- Temperature: stable cold for Arctic char; wrong temperature stresses broodfish and egg quality.
- Several brood groups: different light cycles → staggered spawns → more continuous egg supply.
- Cost: more broodstock space, power for light/cooling, skill and strict biosecurity between groups.
In practice many commercial salmonid hatcheries combine both: controlled broodstock to get eggs when needed, frozen milt as backup, and incubation at a chosen temperature to fine-tune hatch date within the °D window. The sizing calculation (steady inventory) then becomes a target to approach — not a law of nature. Without egg banking or cycle control you must instead size incubators, fry tanks and staff for the peak season and accept lower utilisation the rest of the year.
Example: a salmonid farm (rainbow trout, salmon or Arctic char) that wants food fish every month needs either light-/temperature-controlled broodstock with groups out of phase, bought/eyed eggs from several windows, and/or planned incubation time — otherwise hatch and grow-out clump. See temperature, life cycle, biosecurity and species pages. Orientation — not a breeding protocol.
Sources/overview (selection): FAO aquaculture development guidelines; Wedemeyer, Fish Hatchery Management; Piper et al., Fish Hatchery Management; Timmons & Ebeling, Recirculating Aquaculture Systems; established practice on photoperiod/broodstock and milt cryopreservation in salmonids. The sizing calculator is orientation — not a hatchery project or species-specific protocols/doses.