Dr Mustapha ABA, Aquaculture Scientific Expert, Fish Nutrition. Rabat. Morocco
The success of an aquaculture project depends on several factors and decisions made by its owner, whose expertise is essential in this sector. These include the possibility of taking biometric measurements on fish, a process that provides information on the evolution of the production cycle and facilitates the choices made to improve performance, as well as recognizing the homogeneity or heterogeneity of batches of fish.
1- Introduction
Biometrics is a recommended practice for monitoring aquaculture production, and is considered a simple, fast and extremely effective procedure. The costs of its implementation are also low, since the materials required are not as expensive.
Nevertheless, many aquaculturists still have doubts as to whether it is really necessary to carry out the procedure, as well as its benefits or how to carry it out properly. In order to learn more about the practice, it is important not to compromise the health of the animals, as inadequate management can lead to losses due to fish mortality.
This article, presents some information on biometrics in fish, from defining the practice and its importance, to the technique of carrying it out, with the hope that for African fish farmers, this article will provide them with technical assistance, as biometrics in Africa is unfortunately a practice that is only carried out in scientific research and not in practice in most fish farmers.
2- Definition of biometrics in fish
The term biometrics, bio = life and metric = measured, is the science of measuring living things, a scientific basis for using metric data to statistically study the physical characteristics that indicate the development of fish in a given production unit.
The aim of this practice is to identify problems in the development of fish, closely related to feeding, i.e. the rate of feeding in relation to weight gain. In this way it is possible to make modifications that improve the development of the farm and, consequently, generate more positive economic results for the fish farmers.
3- Importance of biometry in fish farming
It is clear that the performance of biometrics in fish is fundamental to reducing the risks associated with the practice of fish farming. The procedure allows the fish farmer to monitor the development of the fish, identifying if there is a problem that may cause economic damage.
This practice also makes it easier for the farmer to optimise the growth of his fish, ensuring that the quantity of feed is always in accordance with the conditions observed in each of the production ponds and within the limits of the feed manufacturer’s indication. As a result, aquatic animals will have good characteristics and qualities in the consumer market, which will help to increase their commercial value.
4- Frequency of biometry in fish
According to several recommendations, biometrics should be taken every two weeks or at least once a month. Ideally, biometrics should be taken every two weeks; it is advisable to do them on the same day of the week, which creates a healthy routine. The best time is in the morning, before the first ration, preferably a few hours before, which allows the handled fish to rest and feed after the biometry.
5- Scaling
Maximum care in handling is essential, as any injury to the animals can contribute to the development of disease and may result in the death of the fish. To start the biometric process, you must first catch the fish. The use of nets is recommended for this purpose.
The definition of the sample and its reliability is one of the most complex statistical processes, the main reason is that the specific coefficient of variation is unknown, because each crop has particular characteristics that make it impossible to standardize, however, there is a statistical device that defines a sample with adequate reliability, that is to say, apply the square root to the fish population. Example for a number of fish of 1024 would require a sample of 32 fish.
6- Precautions to be taken
It is very important to refine a quick and efficient procedure that will allow fish sampling to be carried out with minimum impact on the total population. The sample should be treated carefully, using rubber gloves so as not to affect the mucous membrane of the fish skin and to keep the fish in clean and oxygenated water, in general it is not necessary to use anaesthetics unless the sample is very large.
7- Materials needed for the procedure
The materials needed to perform biometric measurements can be available to all aquaculturists because of their non-exorbitant cost and that the aquaculturist can manufacture himself on his farm, among these materials are :
- Ichtymeter: preferably portable so that management can be carried out next to the production unit in a simplified and quick way, because these animals do not survive out of the water;
- Weighing scale: for fish handling and biometrics, a precision scale is required.
- Annotation material: notebook, notepad, where the data obtained are written down for future evaluation.
- Net of Fish, for the capture of samples.
8- When to perform Biometry
In order to reduce the stress on the animals, generated by all the handling, moving and catching of fish to carry out this procedure, it is indicated that it is carried out in the first hours of the day.
At present, the temperature and relative humidity of the air, as well as the incidence of the sun’s rays, are at less aggressive levels for these organisms of aquatic life. In addition, it is important to stress the importance of carrying out this procedure before the first feeding session of the day.
9- Calculations
Now that the weighing has been completed, it is time to evaluate the data collected. The first step is to calculate the sample weight using :to calculate the average individual weight of the fish in the sample. Use it for this :
average individual weight = sample weight ÷ number of fish sampled
With this value, the total biomass in the sampled tank can be determined using the following formula :
Total biomass = average individual weight x number of live fish stored in the pond or tank.
Note: Remember to discard dead fish observed throughout the production cycle in each sampled pond to arrive at more accurate biomass values.
10 – Analyses
With the values obtained and calculated, it is sufficient to check the reference tables and make the necessary adjustments in the fish feed, taking into account the parameters indicative of the water quality of the ponds or basins and the water temperature. In addition, it is possible to understand the course of the activity, such as weight gain from one period to the next.
11- Conclusion
Biometrics involves weighing samples of fish or fry, which are being reared, in order to calculate the total biomass. From this sampling, the producer can calculate and determine the amount of feed to be fed to the fish on a daily basis based on tables provided by the feed producers. In addition to monitoring health status to avoid production losses due to disease or poor feeding. It also allows the producer to have a forecast of the time needed to fatten up to the ideal commercial weight, and the amount of feed needed during aquaculture production.
