The FCR (the Feed conversion rate) describes how much feed an animal needs for growth, i.e. the weight gain per feed weight achieved by farm animals in fattening.

It is a simple indication of the efficiency of converting feed to body weight. The required amount of feed per 1 kg of weight gain during fattening is usually specified (so-called feed conversion rate, FCR). The FCR depends primarily on the animal species, the composition and quantity of feed used (energy content, protein content, etc.), but also on other husbandry parameters, such as: Housing density, water temperature, age of animals.

Compared to other farm animals, a very low FCR of approximately 1 to 2 can be achieved for established fish species in optimized aquaculture with pelleted feed, since fish are often more efficient feed converters. Atlantic salmon, for example, is considered extremely efficient and requires only slightly more than 1 kg of feed (dry weight) per kg of growth (wet weight).

The required amount of fish in the form of fish meal and fish oil in the feed per kg of target fish produced is determined as the fish-in-fish-out ratio (FIFO). „Fish-in-fish-out ratio“). According to calculations, the Norwegian salmon industry has a FIFO of approximately 1.

Additional information on feed conversion ratio (FCR):

The feed conversion ratio is significant not only from an economic perspective but also from an ecological one. A low FCR reduces nutrient inputs (nitrogen and phosphorus) into water bodies and lowers the ecological footprint of aquaculture. Modern aquaculture research is increasingly focusing on alternative protein sources to further improve sustainability. These include insect meal, algae, and single-cell proteins, which can replace traditional fish meal.

The calculation of the FCR can vary depending on the context. In the scientific literature, a distinction is sometimes made between the “economic FCR” (total feed intake / total biomass gain, including dead animals) and the “biological FCR” (only for the animals actually harvested). In fish, the FCR is also temperature-dependent, as they are cold-blooded animals and can maximize their metabolism—and thus feed conversion—at optimal temperatures.

Sources beside others: FAO (Food and Agriculture Organization of the United Nations) Technical Papers on Aquaculture; Journal “Aquaculture”; Möbius, W. (2021): Understanding Aquaculture.