A study from the Global Aquaculture Alliance Publications concluded: “Based on the movement of food through the intestines of whiteleg shrimp, shrimp consume food faster when at 32 degrees Celsius.”
The rate of consumption and digest feed varies with the temperature of the culture environment and other factors. Laboratory studies and actual experiments by researchers show that the eating process of whiteleg shrimp will be affected by different water temperatures.
Experiment in the laboratory
Experiments carried out in a laboratory at Kasetsart University, Thailand showed that several empty gut shrimp weighing 12g were placed in a tank filled with purified seawater to assess the amount of food passing through the shrimp’s gut at temperatures of 24, 26, 28, 30, 32 and 34 degrees Celsius with normal shrimp farming conditions.
And the stages are recorded as follows:
- When food is first observed in the intestine
- About half of the intestine
- When the intestines are full, before the stool is passed
- When the stool begins to be excreted
- When the intestines begin to empty
- When the intestines are completely empty
Feed was applied at 3% of body weight according to the food table developed by Kasetsart University. Therefore, the applied food intake was 1% of body weight per meal in three daily meals. Food such as feces, peas and leftovers are vacuumed before each feeding.
Experiment results
For most treatments, it takes only 5 minutes to see feed in the intestines after eating at first, but a significant difference in the rate of digestion begins to appear after that. For example, it takes up to 55 minutes at 24 degrees Celsius compared to 20 minutes at 34 degrees Celsius for shrimp intestines to fill. Once the stools begin to be passed, the difference increases even more, as this takes up to 105 minutes at 24 degrees Celsius compared to 35 minutes at 34 degrees Celsius.
Real test
Evaluation of feed consumption using feed trays at different temperatures was carried out during the 2010 summer cycle.
The experiments were carried out in 8 pounds with an area of 0.25 ha, stocking 150 fish/m2. Evaluation when feed consumption increased sharply (at average weight 6g and fed at 3.5% body weight) and ended at harvest (14g weight and fed at 2.5% body weight).
The feed table was used as a reference for feed dosage, but the number of feed trays was preferred for the daily feed adjustment. Only 4% of the daily intake is put in the tray, the rest is kept.
Feeding at high temperature
Feed was applied at the same dose to the ponds at 6am, 10am, 3pm and 6pm at different temperatures. Temperatures were recorded before each application, and feed trays were checked. 1 to 3 hours after feeding. Feed dosage was increased to a ceiling 30% higher than the corresponding levels in the feed table.
The results in the three temperature ranges in Table 2 show that at 32-34 degrees Celsius, leftovers are never found, while in the 26 to 28 and 29 to 31 ranges, the waste is consumed. Feed intake is considered to calculate the appropriate feed dose.
The time it takes for food to pass through the digestive tract of shrimp at 6 test temperatures under laboratory conditions
| Stages of shrimp intestines (minutes) | Temperature (oC) | |||||
| 24 | 26 | 28 | 30 | 32 | 34 | |
| Feed is observed in the gut | 15 | 5 | 5 | 5 | 5 | 5 |
| Half of gut | 20-30 | 15-20 | 15 | 10-15 | 10-15 | 10 |
| Full gut | 50-55 | 25-30 | 25-30 | 20-25 | 20-25 | 15-20 |
| Begin to excrete feces | 90-105 | 35-60 | 35-55 | 30-45 | 30-45 | 20-35 |
| Starting to empty gut | 150-165 | 100-105 | 95-100 | 90-100 | 75-95 | 75-90 |
| Completely empty gut | 225-240 | 210-220 | 180-200 | 180-190 | 140-150 | 135-140 |
Feeding at high temperature
During the summer cycle, it has been observed that feeding at 32°C or higher can produce excessive vegetative growth, perhaps due to the amount of nutrients released from the feed and the accumulation of a lot of organic matter at the bottom. As a result, a mass of dead algae accumulates on the pond surface. This situation becomes dangerous when excess feed causes the presence of harmful compounds such as Nitric and the proliferation of Vibrio and other pathogenic bacteria, which causing shrimp mortality
It is worth mentioning that shrimp in some ponds of the experiments that were fed only 3 times/day had better feed conversion and survival rates than shrimp in ponds that were fed 4 times/day, probably due to the remove of 3pm dose, when the temperature peaks above 32°C. With less feed being used, farming conditions as well as shrimp survival rates are improved.
Consume feeding trays at different temperatures. Feed dosage is calculated from the Data Feed Table using the Information below
|
Time |
Temperature | ||
| 26-28 | 29-31 | 32-34 | |
| After 1 hour
After 2 hours After 3 hours |
10-20 5-15 0-2 |
2-5
0-2 0 |
0 0 0 |
Conclude
Nutritionists at Kasetsart University have found that the ideal temperature for shrimp to best digest nutrients is between 29 and 31 degrees Celsius, which coincides with the best feed conversion range observed in this experience. According to the experiments described here, shrimp feed digestion at temperatures between 24 and 28 degrees Celsius can take 3-4 hours, giving the interval between each feed can be as long as 5 -6 hours to allow shrimp to fully digest and consume feed for each amount.
On the other hand, at temperatures higher than 32 degrees Celsius, digestion is much faster and food consumption can be higher. However, there is danger in increasing the feed dosage to the extent that it can lead to higher organic matter concentrations in the pond bottom, increase of plant and disease-causing bacteria populations. Finally, it is important to avoid feeding at temperatures above 32 degrees Celsius, under improved production and pond conditions.
