HATCHERY Feed & Management Vol 8 Issue 1 2020

Page 26


The future of fish grading is here Albert Ingi Haraldsson, Vaki

Grading fish in aquaculture is extremely important and its advantages are numerous. An ungraded batch of fish typically displays a normal distribution. The normal distribution, sometimes referred to as the bell curve, has two main characteristics - the mean, or expectation of the distribution, and the standard deviation. The coefficient of variation (CV) is defined as the ratio of the standard deviation to the mean. It shows the extent of variability in relation to the mean of the population. It’s a common practice to grade when the CV has reached 30%. One of the objectives of grading fish is to split the fish up by size to get a certain percentage or biomass in each grade in order to utilize the farm to its fullest. To achieve this, the grader needs constant finetuning based on results from the counter. This can be difficult and time consuming and often results in an unsatisfactory output. VAKI has been working on making the grading process in hatchery simpler, more practical and more automatic. For this purpose, a system was created called SmartFlow.

Hatchery Feed & Management Vol 8 Issue 1 2020

Grading challenges Traditional industrial grading consists of a pump, a grader and a counter. The pump transports the fish from a tank to a grader. The grader divides the fish based on body thickness. Next, the fish flows though a counter which counts the number of fish in each grade separately. The system falls under the category of a multi input, multi output system (MIMO). The system is sensitive to any changes. A small change to the input can cause a dramatic change in the final output and it’s not uncommon that hundreds of thousands of fish are graded in one session and the size range varies from a few grams to a few hundred grams. The process of grading fish also falls under the category of a nonlinear system, which in layman’s terms means the output does not react the same to changes in the input throughout the process. All these factors contribute to making the grading process fairly complicated and hard to tune. Here is where SmartFlow comes in.

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