Fish shelters are a simple, inexpensive addition to your aquaponics system that reduce fish stress, improve growth rates, and increase the biological surface area for beneficial bacteria — a genuine win on every front.
In nature, fish spend significant time near cover — submerged logs, rocks, aquatic vegetation, and undercut banks. Without any shelter in a bare aquaponics tank, fish are continuously exposed, which elevates cortisol (stress hormone) levels chronically. Chronic stress suppresses the immune system, reduces feed conversion efficiency, and slows growth. Adding simple shelters addresses all of this at minimal cost.
Why Do Fish Need Shelters in Aquaponics?
Stress Reduction
Fish kept in bare tanks without hiding places show measurably higher cortisol levels than fish with access to shelter. Elevated cortisol:
- Suppresses immune function — stressed fish get sick more easily
- Reduces growth rate — energy goes to stress response rather than body mass
- Reduces feeding motivation — stressed fish eat less
- Increases aggression between fish — particularly in species with territorial tendencies
Providing shelter normalises fish behaviour and reduces cortisol, directly improving health, growth, and feed conversion.
Natural Behaviour Support
Most aquaponics fish species have evolved to hide periodically — from predators, from dominant individuals in their group, and simply as a resting behaviour. Denying this instinct creates low-level chronic stress. Fish with access to shelter:
- Feed more confidently
- Establish stable social hierarchies without constant aggression
- Show less surface-skimming (a stress response often confused with low oxygen)
Additional Biofilm Surface Area
Every hard, wet surface in your system develops bacterial biofilm — beneficial nitrifying bacteria that process fish waste. Shelters add significant surface area to your fish tank, increasing bacterial colonisation capacity. This is particularly valuable in systems where grow bed volume is limited relative to fish load.
What Materials Work for Aquaponics Fish Shelters?
Food-Safe and Fish-Safe Materials
Any shelter material that goes into your fish tank must be:
- Non-toxic: No treated timber, galvanised metal, copper fittings, painted surfaces, or non-food-grade plastics
- pH neutral: Limestone and concrete can raise pH — seal or avoid
- Durable in water: Won’t degrade, leach, or break down over years of submersion
Best Shelter Options
- PVC pipe sections: The most commonly used shelter in aquaponics. Food-grade PVC is completely fish-safe, cheap, available at any hardware store, and lasts indefinitely. Use 90–150 mm diameter pipe cut into 30–50 cm sections. Drill holes in the top for water circulation. Lay horizontally on the tank bottom.
- Food-grade plastic containers and trays: Inverted with entry holes cut — create cave-like shelters. Use black containers to reduce light inside the shelter, which fish prefer.
- Natural rock: Smooth river stones or flat slate stacked to create crevices. Completely inert and natural-looking. Avoid limestone (raises pH).
- Terracotta pots: Unglazed terracotta is fish-safe, pH neutral, and provides excellent biofilm surface area. Place on their side or stack to create crevice shelters.
- Aquatic plant bunches: Dense floating or rooted aquatic plants (not in the fish tank typically, but aquatic plants in a connected pond section) provide excellent natural cover for less intensively managed systems.
How to Design Shelters for Your System
Quantity and Coverage
Aim for one shelter unit per 3–5 fish. Shelters should occupy 20–30% of the tank floor area — enough to provide meaningful cover without restricting water circulation or making observation and netting difficult.
Positioning
- Place shelters away from the main water return (where water enters the tank) — fish prefer calmer areas near shelter
- Distribute shelters across the tank rather than clustering in one corner — this prevents dominant fish from monopolising all cover
- Position so you can still net fish when needed — leave a clear section of tank for catching operations
Cleaning and Maintenance
Shelters accumulate detritus underneath them. Every 2–4 weeks, shift shelters and vacuum accumulated waste from beneath. Don’t scrub the outside surfaces — beneficial biofilm builds up on shelter surfaces and should be preserved.
Do All Fish Species Benefit from Shelters?
Yes, but the benefit varies by species:
- High benefit: Murray cod (ambush predators that strongly prefer cover), catfish species (nocturnal, hide by day), perch species
- Moderate benefit: Silver perch, jade perch, barramundi — all appreciate cover but don’t require it as strongly
- Lower benefit: Tilapia (less shelter-dependent in groups), goldfish and koi (less stress-sensitive but still appreciate cover in larger ponds)
Frequently Asked Questions
Won’t shelters make it harder to net fish?
Somewhat — fish will retreat into shelters when stressed by netting. The practical approach is to remove shelters temporarily during harvest operations, net fish efficiently, then return shelters. For scheduled harvests, this is a minor inconvenience worth the year-round welfare benefit.
Can I use regular PVC plumbing pipe for fish shelters?
Standard grey PVC electrical conduit and white plumbing PVC are both fish-safe at normal aquaponics temperatures. Avoid PVC with UV stabilisers that may be treated with different additives, and avoid any painted or solvent-welded fittings inside the tank. Plain, unjoined PVC pipe sections are the safest option.
Do shelters affect water quality?
Positively, if managed properly. Shelters add biofilm surface area (beneficial bacteria) and reduce fish stress (which reduces stress-related immune responses and disease). Negatively, if neglected: accumulated waste under shelters can create localised low-oxygen zones. Regular light vacuuming under shelters prevents this.
How many shelters do I need for 20 fish?
For 20 fish, 4–7 shelter units is a reasonable range. The goal is that every fish can be near cover simultaneously if they choose. Provide a variety of sizes if you have mixed-size fish — larger shelters for dominant individuals, smaller ones for juveniles.
Want to build an aquaponics system that promotes healthy, fast-growing fish alongside abundant plant production? Our complete aquaponics training covers fish welfare, tank design, and everything you need to run a productive system.