Water temperature is one of the main environmental factors conditioning fish feeding, metabolism, and growth. As ectothermic animals, their body temperature depends on the environment, but their response to a thermal change is not the same for all species or at all times of the year.
When the temperature drops, the first reaction should not be to automatically reduce the ration. First, it is necessary to answer a fundamental question:
Does the new temperature bring the fish closer to its optimal range or move it further away?
In cold-water species, such as rainbow trout, a drop from summer temperatures above 20 °C to more favorable values can improve appetite, reduce thermal stress, and recover productive efficiency. On the other hand, if the water continues to cool below its suitable range, metabolic activity, digestion, and feed intake will begin to decrease.
In temperate or warm-water species, such as gilthead seabream, European seabass, or tilapia, cooling can cause an earlier or more pronounced reduction in intake. The strategy must always be adapted to the species, size, farming system, and starting temperature.
Absolute temperature and rate of change
Not only does the recorded temperature matter, but also how quickly it changes.
A gradual drop allows the fish to progressively adapt its metabolism and behavior. Conversely, a sudden drop can temporarily reduce the feeding response, even when the final temperature falls within an acceptable range.
During a thermal transition, the following should be monitored together:
- Temperature at the depth where the fish are located
- Dissolved oxygen and saturation percentage.
- Rate of thermal change.
- Behavior before and during feeding.
- Time required to consume the ration.
- Presence of uneaten feed.
- Trends in biomass, growth, mortality, and FCR.
Cold water can hold more oxygen than warm water, but this does not automatically guarantee good availability. Biomass, flow rate, water renewal, aeration, and organic matter also determine the oxygen that the fish will actually have.
The risk is not just overfeeding
When the temperature strays from the optimal range and appetite decreases, maintaining the same ration can lead to uneaten feed, deteriorate water quality, and increase the cost per kilogram of biomass produced.
In these cases, the FCR can worsen because the amount of supplied feed that is not converted into growth increases. In systems with lower water renewal, the degradation of organic matter can also consume oxygen and promote the accumulation of nitrogenous compounds.
However, reducing feeding too much also carries consequences. If the cooling brings the fish from a state of heat stress toward more favorable temperatures, an automatic reduction of the ration can limit a period of growth recovery and waste productive capacity.
Therefore, feeding must respond to the fish and the real farming conditions, not solely to the calendar.
How to adapt feeding during thermal transition
- Use feeding tables as a starting point: Feeding tables are a reference tool, but they must be adjusted according to actual temperature, biomass, available oxygen, and the observed response in each culture unit.
- Measure under representative conditions: Temperature and oxygen should be measured at the depth and time at which the fish are fed. A single reading taken at the surface may not represent the conditions experienced by the entire population.
- Adjust the ration progressively: In the face of a thermal change, it is preferable to make gradual corrections and check the response before making major reductions or increases. Sudden variations can make it difficult to interpret actual consumption.
- Observe feeding behavior: The intensity of the feeding response, consumption speed, fish dispersion, and the presence of uningested pellets provide immediate information. In systems where possible, cameras, sensors, or feeding trays help improve precision.
- Review frequency and timing: There is no universal schedule for all species and systems. Feeding should be concentrated during periods with stable temperature and oxygen conditions, avoiding times when the fish’s response is low.
- Periodically update biomass: An incorrect biomass estimate can be mistaken for an effect of temperature. Reviewing growth, survival, and size distribution allows for a more accurate ration calculation.
The importance of an adapted diet
When metabolism and consumption change, every pellet becomes even more important. The diet must provide digestible nutrients and maintain a proper balance between protein and energy, preventing a reduction in intake from compromising nutritional supply.
Physical quality is also essential. A uniform pellet with good stability and low levels of dust and fines facilitates a more controlled distribution and allows for a better assessment of the feeding response.
The grinding, micronization, and extrusion processes used by Dibaq Aquaculture help optimize the physical characteristics of the feed and nutrient utilization. Furthermore, raw material selection and formula design are adapted to the nutritional needs of the species and its production stage.
The goal is not simply to supply more or less feed, but to deliver the right amount of an appropriate diet when the fish can best utilize it.
Turning transition into an opportunity
Thermal transition should not be managed with an automatic rule. In some situations, it will be necessary to reduce the ration; in others, maintain or gradually increase it to take advantage of the recovery in appetite and growth.
The decision must be based on the species, starting temperature, rate of change, available oxygen, and fish behavior.
With constant observation, flexible management, and high-quality diets, it is possible to reduce waste, protect water quality, and maintain productive efficiency during seasonal changes.
Dibaq Aquaculture develops nutritional solutions adapted to each species and production stage, supporting producers to transform environmental changes into more precise feeding decisions.