Heath trays, also known as vertical incubators, are among the most widely used egg incubation systems in salmonid hatcheries. Multiple trays are stacked vertically, allowing large numbers of eggs to be incubated within a relatively small floor area. Water typically enters at the top of the stack and flows downward through each tray, providing oxygen and carrying away waste products.
The design offers excellent space efficiency and is particularly suited for species with relatively large demersal eggs, such as Atlantic salmon, rainbow trout, Arctic char, brown trout, and Pacific salmon species. Individual trays can be removed for inspection, grading, disinfection, or egg picking without disturbing the entire incubation system.
Typical loading densities range from several thousand to tens of thousands of eggs per tray, depending on egg size and hatchery practices. A single Heath stack may hold hundreds of thousands of eggs, making the system highly scalable for both small hatcheries and commercial facilities producing millions of fry annually.
Advantages and requirements
Advantages include high egg density, simple construction, easy inspection, good water distribution, and proven performance over decades of commercial use. However, careful management of flow distribution and routine removal of dead eggs are important to prevent fungal outbreaks and maintain high survival rates. See also egg incubators, egg disinfection and biosecurity.
Typical species
- Atlantic salmon (Salmo salar)
- Rainbow trout (Oncorhynchus mykiss)
- Arctic char (Salvelinus alpinus)
- Brown trout (Salmo trutta)
- Chinook salmon (Oncorhynchus tshawytscha)
- Coho salmon (Oncorhynchus kisutch)
Typical design parameters
| Parameter | Orientation |
|---|---|
| Water flow | ~2–10 L/min per tray |
| Egg loading | ~5,000–50,000 eggs per tray |
| Dissolved oxygen (DO) | > 8 mg/L (typically near saturation) |
| Temperature | Species dependent; salmonids commonly about 4–12 °C |
| Common hatchery scale | ~0.1–10+ million eggs |
| Stack geometry (typical data) | Often 8 trays/stack; height about 1.6–2.0 m |
Teaching ranges. Flow, load and temperature depend on species, egg size and hatchery standard — not fixed rules.
Simple tray-count sizing
Number of trays ≈ (number of eggs / eggs per tray) × safety factor, where the safety factor is often about 1.1–1.5 (spare, uneven loading, picking). Number of stacks ≈ trays / trays per stack (e.g. 8).
Example: 1,000,000 Arctic char eggs, 25,000 eggs/tray, safety factor 1.25 → trays = 1,000,000 / 25,000 × 1.25 = 50 trays. With 8 trays/stack ≈ 7 stacks (rounded up). The same logic is used in the calculator under Egg incubators (choose stacked trays).
- Check flow per tray so DO is held and dead zones are avoided.
- Pick dead eggs routinely; fungus spreads quickly in dense trays.
- Darkness/low light, stable temperature and biosecurity between stacks.
Sources/overview (selection): Wedemeyer, Fish Hatchery Management; Piper et al., Fish Hatchery Management; established salmonid hatchery practice; see also Egg incubators. Orientation — not a supplier specification or protocol.