## 1 Introduction  
Pikeperch is a predatory fish that lives in fresh water, belongs to the family _Percidae_ (order _Perciformes_), and is found in Europe and North America. This fish is appreciated by consumers due to its white and tender meat, and low quantity of bones. The muscle tissue of pikeperch is lean (below 2% fat) and contains a high amount (approx. 20%) of highly digestible protein (approx. 98% of digestibility) with a higher content of exogenous amino acids than other popular fish species such as herring, perch, roach, bream, and eel [1], which makes this fish a valuable food product. There is a growing demand from retail and the HoReCa sector (hotels-restaurants-catering) for pikeperch [2] and therefore the influence of cooking methods on the quality and nutritional value of the fish is worth investigating.  
Microwave and sous-vide cooking are thermal treatment methods which can be used in both the household and under industrial conditions. As all cooking methods, they are used to make a food safe for consumption and to change the sensory quality of food products by making them more attractive for consumers. In the sous-vide method, a raw product is vacuum-packed in plastic pouches and subjected to heating at precisely controlled temperatures [3]. According to [PERSON] [4], vacuum-packaging prior to cooking has many benefits, which include the efficient heat transfer from the medium (water or steam) to the food and prolonging the shelf-life by: (1) reducing the risk of recontamination during storage and (2) by lowering the extent of oxidation and off-flavours occurrence. Moreover, vacuum-packaging prevents evaporative losses of flavour volatiles and moisture during cooking, thus increasing cooking yields, and reduces aerobic bacterial growth [4] as compared with traditional cooking methods. With this technique, it is possible to extend a product's shelf-life up to 90 days if stored below 2.5 \({}^{\circ}\)C [4]. Sous-vide food can be regarded as ready-to-eat products and after termination of the cooking process they can be held in a chafing dish (so called \"cooked-hold\" or \"cooked-served\" sows-vide mode) at a min. 54.4 \({}^{\circ}\)C until served, or as ready-to-heat products (\"cook-chill\" and \"cook-freeze\" sows-vide mode), which can be stored at a low temperature or in a freezer and reheated before eating [5].  
Microwave ovens are common devices in households worldwide and can be used for both preparing raw food products for consumption or reheating ready-to-eat meals. Microwave cooking being a volumetric heating, it allows to increase the temperature of a foodstuff quickly with low energy consumption; however, it can generate hot and cold spots in a dish and requires the use of specific types of packaging or containers [6]. Microwave cooking was used in our previous study in which the effect of thermal treatment on the fatty acid profile in northern pike was investigated [7]. It was noted that microwave cooking decreased the proportion of saturated fatty acids, increased the proportion of total polyunsaturated fatty acids (PUFAs), n-3 and n-6 PUFAs, compared with fresh fillets, and enabled fish products to obtain a more beneficial n-6/n-3 ratio than frying. Therefore, it was concluded that it was a better technique for pike fillet preparation in households that pan frying and steam cooking. However, despite the lack of scientific evidence, there is some consumer concern regarding the use of microwave ovens to prepare dishes [8]. In light of this, the sous-vide technique might be a promising alternative for preparing fish meals intended to be immediately consumed or even to be stored and consumed later. Therefore, in the present study, microwave cooking was compared with the sous-vide technique used to prepare pikeperch fillets. The effects of these two cooking methods were compared in terms of their impact on proximate and fatty acid composition, colour, and microbial and sensory quality of wild pikeperch fillets.