Keeping fish and plants together has some basic requirements and important parameters.
Water temperature is a very important parameter. If the water temperature gets too high it will knock the plant performance back. The ideal temp for both plants, Jade Perch and Tilapia is 23C ( 73F) as it goes higher or lower the performance of both plants and fish drops off. Tilapia will still be fine in water up to 30C (86F) and a little way beyond. Plants will also survive but do much less well, particularly lettuce and the like.
The system water temps do not necessarily follow exactly the outside air temp although they will gradually trend upwards in a succession of hot days. We see weeks of 33 -35C (90 - 95F) here in our South Queensland summer, our nights are usually average around 21C (70F) so over the summer the water temp gradually climbs to level out around 28 - 30C (83 - 86F) Not so bad. Everything works just fine in that temperature range.
The system water in our Aquaponics garden is the nutrient and dissolved oxygen transport vehicle as well as providing moisture for the plants and fish. In a well designed Aquaponics garden nutrient and dissolved oxygen are continuously moved around and made available throughout the Aquaponics system. Obviously both plants and fish will do much better when both dissolved oxygen and temperature are at or close to ideal levels.
This last summer we had one week of temps above 40C (104F) with one Saturday to 46C (115F) which was just an unbelievable day.
Hot mate, you could fry an egg on the footpath!
That day my water temps got to 34C ( 95F) and I lost a number of fish. All big guys too which was very upsetting. I was away for the day so could not do anything about it till I got home just before dark to find fish gasping at the surface and a number of dead fish.
Above 30C (86F) the ability of the water to hold dissolved oxygen drops off rapidly so, result equals fish deaths and plant destruction. Water will only hold half the saturation of oxygen at 30C (86F) that can be held at 0C (32F).
Interestingly, if you can maintain reasonable root zone temps the plants may wilt a bit during a very hot day but will recover rapidly once the evening comes and will still grow and bear fruit in the case of tomatoes and cucumber for example.
So....root zone temperature control is the holy grail of delivering excellent results in your Aquaponics system.
Temperature control is equally important in cold climates, winter conditions. Depending on where you are in the world this can be challenging or not so bad. We will deal with that in another post.