Surf'n'Turf Shack stack

For an improved version, see Surf and Turf stack v2[blueprintnotincluded.com]
On top is an automated Pacu farm along with a cooking station, below is a stackable Hatch ranch.

For the TL;DR; version (along with the mirror automation), see Surf and Turf stack[blueprintnotincluded.com]
Each hatch ranch is 72x5 to support 8 hatches (enough to feed 5 duplicants barbeque or 7.5 duplicants surf'n'turf with 5 broiler pacu per duplicant) and new ranches may be added below as required.
The egg hatchery is 9x5 and must be above the hatch ranches. In my build I put a couple of coal generators and and auto-sweeper in a sealed room behind the egg hatchery to turn the coal into power.
The pacu farm is 24x9 and could be built beneath the ranches (although that limits expansion). It is possible to make the large tank smaller with a corresponding reduction in the number of laying pacu.

This is an automated three stage Pacu farm optimised to provide the most Pacu Fillets for the least resources.

In the small tank a single wild Fry Egg hatches and is fed 1kg of Algae each cycle to become tame as quickly as possible and lay tame Fry Eggs. Conveyor Loader: (set after Fry hatches) Fry Egg (all types), Pacu Fillets, Egg Shells
Fish Feeder: 1kg Algae; change to 1kg seeds when Pacu becomes tame
Storage Bin: Sweep Only, normal Fry Eggs (deselect after loaded), 20kg Algae, 10 kg of seeds
Timer: Green 5 seconds, Red 595 seconds, restart immediately after Fry hatches

In the large tank four tame Pacu eat surplus seeds and lays 11 eggs over their lifetime, rapidly increasing the food population. Conveyor Loader: Fry Egg (all types), Pacu Fillets, Egg Shells
Critter Sensor: Below 4 Critters
Fish Feeder: seeds (whatever is surplus)
Storage Bin: low priority, seeds

In the open room excess Pacu are stuffed into a single cell of water where they will generate Pacu Fillets and Egg Shells indefinitely.

Electric Grill: Barbeque & Cooked Fish
Gas Range: Surf'n'Turf
Refrigerator: Barbeque, Cooked Fish, Meat, Pacu Fillet, Surf'n'Turf
Solid Filter: normal Fry Eggs

A Conveyor Loader (or two) can be added to automatically ship Coal (from the Hatch ranch) and Egg Shells to the appropriate location.

Two possible modifications to the tanks I've thought of.

1. Only have a single large tank containing 8x4 water. Requires moving the automated auto-feeder to the attic space and restricting access until the pacu becomes tame. (At which point the auto-feeder may be deconstructed.)
   
2. Make the small tank 2x4 (vertical) and connect it to the large tank via a pneumatic door or mesh tile and remove the top tile to connect the two rooms, making a single large room and large tank which can then host 5 laying pacu. Also requires reworking the other buildings.

This design is based on Fully Automated Hatch Ranching By Magialisk.

Each Stable level supports 8 Hatches. Manual operation (no automation or shipping) may be accomplished by replacing the Auto-Sweeper with a Critter Drop-Off and manually sweeping any eggs into a Storage Bin located outside of he Stable. See Magialisk's guide for ideas to use the empty space in the Stables. Conveyor Loader: Coal, Hatch Eggs (all types), Meat
Critter Detector: Below 8 Critters

In the main room Hatch Eggs are sorted by Solid Filter into layers and broilers.

• Broiler (Stone and Sage Hatch) Eggs are put into the larger pit to hatch. When they hatch the Mechanical Airlock will close (if open), drowning the Hatchling.
  
• Layer (Normal Hatch) Eggs are put into the small pit to hatch and mature. If a Stable has less than 8 Hatches the Pneumatic Door to the small room will be open and the Mechanical Airlock closed. But if all stables have 8 Hatches the Pneumatic Door to the small room will be closed and the Mechanical Airlock will be open. When the Hatch jumps into the large pit the Mechanical Airlock will close, drowning the Hatch.

Conveyor Loader: Coal, Meat, Egg Shells
Critter Detector: Below 1 Critter
Solid Filter: Normal Hatch Eggs
Note: the larger pit must contain some water

The small room contains two Critter Detectors. One is set to Above 1 Critter, the other is set to Below 1 Critter. When the room contains one (and only one) Hatch, the entry Pneumatic Door will close and the exit Pneumatic Door will open. When the Hatch jumps down into the open Pneumatic Door, the exit Pneumatic Door will close, forcing them downward into the lowest underpopulated Stable.

Note: this portion of the build is tricky due to the "buried" gates and the automation. Recommend building the top layer from the bottom up and only automating the doors after the rest of the build has been completed. Also recommend locking the access doors after the build is completed to avoid duplicants trying to perform supply errands.

For those interested in Smooth Hatch ranching, see Hatch Morph Ranch[blueprintnotincluded.com]

I'm sure many players have encountered the same challenges I did when starting Pacu farming:

• Set up a breeding room with automated egg extraction and Algae delivery.
  
• Watch as a single wild Pacu eats through 4400kg of Algae to lay 9 eggs.
  
• Decide there has to be a better way and instead retry with Mealwood seeds.
  
• Watch as the wild Pacu eats less than once per cycle so never becomes tame and only lays a single egg.

Neither of these alternatives appears to be viable which makes Pacu farming difficult until you understand the mechanics of Pacu feeding. Pacu Fry start with a store of 450 kCal which decreases over time based upon their metabolism. 140kg of Algae or 250g of seeds provides 100 kCal (1 seed = 1000g).
Below 450 kCal the Pacu becomes Hungry and will eat from the Fish Feeder until it reaches 500 kCal or no food remains.* Eating from the Fish Feeder also causes the Wildness of wild Pacu to decrease by 15% over the next cycle (instead of increasing by 5%). Note: I have observed cases where Fry will "forget" they have eaten from the Fish Feeder and lose the Wildness buff.

Given unlimited food, wild Fry will only eat once before maturing while wild Pacu will only eat every other cycle - which significantly increases the number of cycles before becoming tame. Therefore it is important to restrict the amount of food available to wild Fry and Pacu to ensure they eat every cycle and therefore speeding up the taming process.

However, once a Pacu is tame it is important for it to eat from the Fish Feeder every cycle and not reach 0 kCal - as in either case the Pacu becomes Glum and loses the +60% Reproduction buff.

* During my testing I've observed tame Pacu consuming 280kg of Algae per cycle so there may be an additional mechanic.