Aquaculture in Probably Stolen lets you turn fish farming into another source of products and income, but a tank full of fish isn't automatically profitable. Understanding how water, feeding, and growth interact is the key to keeping your stock alive and making the most of each harvest.
Jump To Section:
How to Unlock Aquaculture
How to Keep Your Fish Alive
All Fish Species and Their Uses
How to Breed and Grow Fish
Harvesting Fish and Making Money
Why Your Fish Keep Dying
How to Unlock Aquaculture in Probably Stolen
You can unlock aquaculture by choosing the Aquafarmer starting scenario or purchasing the Aquaculture upgrade through Joe Wild's Network after unlocking Water Trading.
If you didn't choose Aquafarmer, follow these steps:
- Reach Day 7 to gain access to Joe Wild's Network.
- Purchase Water Trading for 300 Credits, unless you've already unlocked it.
- Purchase Aquaculture for another 400 Credits.
- Collect the starter equipment provided with the unlock.
- Set up your Recirculating Aquaculture System and begin raising fish.
Starting without either trade means the combined unlock cost is 700 Credits before any additional expenses. Your run's price modifiers may affect the amounts shown.
Setting Up Your First Fish Tank
The aquaculture starter equipment includes a Recirculating Aquaculture System (RAS), fertilized Tilapia roe, fish feed, an Energy Cell, water, and basic harvesting tools.
Your first goal is to get the RAS operational:
- Place the RAS in your available workspace.
- Install an Energy Cell. The system consumes 5 power each night.
- Add water to the tank, which holds up to 12,000 mL.
- Install Water Filters in the available filter slots.
- Add the fertilized roe and supply food through the Livestock Feed Dispenser.
- Keep the system powered overnight to begin the growth cycle.
The RAS has four filter slots, making water treatment an important part of the setup. A working tank needs more than enough water to fill it. That water also needs to remain suitable for the fish living inside.
How to Keep Your Fish Alive in Probably Stolen
Fish farming becomes much easier once you understand the three limits that matter most: available water, contamination, and food.
A tank can look properly stocked while still being on course to lose its fish overnight.
Calculate Water Before Adding More Fish
Every adult fish has a minimum water requirement based on its species. The RAS can hold 12 liters, but the amount your fish collectively need depends on what you've stocked.
For example, one adult Tilapia needs 750 mL of water. A tank with eight adult Tilapia therefore requires 6,000 mL to satisfy their combined water needs.
That creates two important thresholds:
- Below 6,000 mL, those eight fish begin losing health because their water needs aren't fully met.
- Below 3,000 mL, the tank falls under half their combined requirement, causing the fish to die.
This calculation only covers water quantity. It doesn't mean eight fish are guaranteed to survive in 6,000 mL if the water is badly contaminated or they're starving.
I'd keep the tank comfortably supplied rather than treating its minimum water requirement as a target.
Watch Organic Waste, Not Just Water Levels
Fish generate Organic Waste as they grow. The amount added overnight depends on their weight, which makes larger or heavily stocked tanks harder to maintain.
Organic Waste becomes harmful at 3% of the tank's volume and lethal at 8%.
For a 12,000 mL tank, those thresholds correspond to:
- 360 mL of Organic Waste: the point where harmful effects begin.
- 960 mL of Organic Waste: a lethal contamination level.
This explains why filling every available space with fish isn't necessarily productive. You may increase your potential harvest while also increasing the rate at which the tank becomes dangerous.
Powered Water Filters reduce contamination overnight, so make sure the RAS has enough energy to operate.
Don't Ignore Hunger
A fish that reaches zero hunger for two nights will die. Feeding is therefore just as important as providing sufficient water.
Healthy fish can also recover from damage. During a powered night, fish with at least 50% hunger recover 10% of their maximum health.
If your fish have already suffered from poor water conditions, restoring food, filtration, and power can give surviving stock an opportunity to recover.
All Fish Species in Probably Stolen and What They're Good For
There are six fish species available through aquaculture. Each has a different purpose, so the best choice depends on whether you want repeatable harvests, useful materials, or additional machine support.
| Fish | Adult Water Need | Main Benefit |
|---|---|---|
| Tilapia | 750 mL | Breeding and regular fish fillets |
| Gutter Tilapia | 750 mL | Removes several water contaminants and resists Organic Waste damage |
| Graft Tilapia | 750 mL | Produces Tilapia Skin Grafts |
| Eel | 1,200 mL | Larger fish harvests |
| Electric Eel | 1,200 mL | Charges batteries overnight |
| Sturgeon | 3,000 mL | Produces Caviar |
Which Fish Should You Raise First?
Regular Tilapia is the easiest starting point because it can reproduce inside the tank. Maintaining breeding adults lets you raise replacement fish instead of purchasing every new batch.
Gutter Tilapia is particularly interesting for water management. It removes Heavy Metal, Chemical, and Physical Contaminants, and Organic Waste doesn't damage it. However, that doesn't make filtration unnecessary for other fish sharing the tank.
Graft Tilapia is more specialized. It produces one Tilapia Skin Graft per 200 g of body weight, but it also takes twice the usual damage from Organic Waste. I'd avoid overcrowding a tank containing this species.
Eels, Electric Eels, and Sturgeon become available through the Aquaculture II expansion, which costs 1,200 Credits. Unlike Tilapia, these species don't breed in the RAS, so replacing harvested fish requires additional stock.
How to Breed Tilapia and Grow More Fish
Tilapia reproduction is what makes aquaculture capable of maintaining its own supply of fish.
Once a breeding pair reaches adulthood and has suitable conditions, it can produce fertilized roe. A roe batch hatches into six fry, creating another generation without requiring you to purchase six individual fish.
How Long Does Tilapia Take to Grow?
The usual Tilapia growth milestones are:
- After 1 night: fertilized roe hatches.
- At 3 days old: Tilapia reaches the juvenile stage.
- At 8 days old and 450 g: Tilapia qualifies as an adult.
- From 27 days old: Tilapia enters old age.
Well-fed adult Tilapia have a 15% chance of breeding each night. This is a chance-based process, so don't expect a new batch of roe every day.
Feeding Tilapia meat can increase their growth rate by 25%, making it useful when you want to shorten the time between hatching and harvest.
Keep Enough Fish for the Next Generation
Harvesting every adult gives you immediate food products, but it also removes your breeding stock.
A better approach is to retain breeding adults while harvesting excess fish as new generations mature.
It's also important to account for the six new fry created by each successful roe batch. As they grow, their water requirements and contribution to Organic Waste increase.
Don't plan your tank around its current population alone. Make sure there's enough capacity for the fish you're expecting to raise next.
How to Harvest Fish and Make Money From Aquaculture
Fish have several potential uses beyond simply keeping them alive. Their value depends on what you raise and which products you collect.
Selling Fish Fillets
You can butcher fish using a knife or use an Auto Butcher to handle processing. The machine can also collect roe, making it useful as your operation grows.
Fish fillets have different sale values depending on their size:
| Fillet Size | Base Value |
|---|---|
| Tiny | 13 Credits |
| Small | 26 Credits |
| Standard | 57 Credits |
| Large | 143 Credits |
These are product values, not guaranteed daily earnings. Your output depends on the fish you harvest, while running the tank still requires food, water maintenance, and power.
How to Get Caviar From Sturgeon
Sturgeon offers a different way to earn money. Rather than relying on breeding, you can use a Surgery Toolset to extract Caviar.
Each jar has a base value of 240 Credits, with a harvest potentially producing up to ten jars. That represents as much as 2,400 Credits in gross product value from a maximum-yield harvest, before accounting for expenses.
However, Sturgeon needs 3,000 mL of water per adult and takes 18 days to reach maturity at 3,500 g. It's a more demanding investment than a small Tilapia operation.
I'd establish a reliable tank before committing space and resources to Sturgeon, especially since they cannot breed to replace your existing stock.
Why Are Your Fish Dying in Probably Stolen?
If fish are disappearing or losing health, check the tank conditions before purchasing more stock. Several different mechanics can cause losses, and adding replacement fish won't solve the underlying problem.
Fish Have No Food or Enough Water
Running out of food for two consecutive nights at zero hunger is fatal. Severe water shortages are even more dangerous, since dropping below half the combined water requirement kills the tank's fish.
Check the Feed Dispenser and calculate how much water your current adult population needs.
The Filters Aren't Keeping Up
Fish continue generating Organic Waste as they grow. If your RAS isn't adequately powered or filtered, contamination can increase until it starts damaging the stock.
Graft Tilapia is especially vulnerable because of its increased sensitivity to waste.
Fish Are Being Left Outside the Tank
Fish cannot be stored outside the RAS overnight without consequences. Adult fish left out overnight die, while fry removed from the tank are destroyed.
Plan transfers and harvesting carefully rather than treating fish like ordinary inventory items.
Your Fish Have Reached Old Age
Fish don't remain productive forever. Once a species reaches its old-age threshold, it has a 50% chance of dying each night.
Regular Tilapia enters old age at 27 days, while Sturgeon reaches that stage at 80 days. Other species have their own aging limits.
Harvesting or replacing fish before they become old helps avoid losing a valuable animal without receiving its intended products.
If you're struggling to maintain clean water for your tanks, our Probably Stolen Water Purification Guide covers how to improve water quality and use purification equipment.
For a new aquaculture setup, I'd focus on keeping a small Tilapia population healthy and breeding before expanding. Once you understand how quickly the tank accumulates waste and how much water your fish require, you can make better decisions about adding specialized species and harvesting for profit.
