Feeding Regimes
Feeding efficiency is affected by the rate at which food is dispersed, the number of feeds per day and the duration of each feed. These factors also play a part in determining satiation. Analysis of the feeding process in terms of the number of pellets delivered is one way of developing an optimal feeding regime. Based on fish size and pellet diameter the number of pellets a fish requires for its daily ration can be estimated and used to examine the influence of feeding techniques.
Number of feeds per day
Using the example of a 1kg fish fed at 1% of body weight per day (31 pellets/fish/day), some consequences of splitting the daily ration into a different number of feeds can be seen above.
Feeding once a day would result in each fish obtaining its full ration (31 pellets) and all the fish would be satiated. If fed twice a day, there would be 15.5 pellets per fish at each meal. In this case, either 50% of the fish would be satiated at each meal or each fish obtains only 50% of its daily requirement in the first feed and the other half at the second meal. At the other extreme, feeding 31 times in a day means that there is one pellet per fish at each meal - either 3% of the fish could be satiated at each meal or each fish obtains around 3% of its daily need at each feed.
Increasing the number of meals thus reduces feeding opportunities through reduction in feed availability. In addition many small meals will result in the formation of dominance hierachies and increased competition leading large size/weight variations, which the farmer wishes to avoid. The dominant fish will ensure that all the food offered with many small meals will mean that the use of waste feed detection systems is not feasible as there will be no waste feed at any of the meals. Similarly, comparision of growth rates and FCRs will have no meaning.
Effect of increasing number of feeds per day.
Feeding varies within the industry from one to three meals per day for those using hand feeding to automatic systems delivering hundreds of small quantities of feed throughout the day. Either system can produce high growth rates and low FCRs as the fish adapt to the preferred system, physiologically and behaviourally.
Depending on fish size, the maximum number of meals per day would be the one which ensures at least one pellet per fish per meal. From numerous studies the optimum number of meals appears to be in the range 1-6 per day to satiation, the actual number depending on the species and water temperature. Except for first-feeding fry, the number of meals does not relate to size as gut evacuation rate appears to be independent of body weight.
With a few large meals stomach capacity could limit the amount of food that could be eaten. However research indicates that salmonids maintain their stomach capacity well below the maximum (0.1-0.25g per 100g body weight as opposed to 5g) in the presence of unlimited food supply. Thus salmonids could consume more than the highest daily ration they are likely to be given in a single meal. Appetite will increase as the stomach empties so that too long a period between meals could lead to reduced growth rates. Feed intake and gut evacuation rates are temperature-linked; as the latter increases so do the former. Consequently more meals should be offered at higher water temperatures - this is common industry practice as may be deduced from the table below.
Number of feeds and water temperature
| Water Temperature (oC) | Feeds per day |
| 0-5 | 1 |
| 5-10 | 2 |
| 10-15 | 3 |
| > 15 | 4 |
