## 7 Fish Processing and Preservation
### Drying  
This method consists of the loss of water that reduces the water activity necessary for microbial growth and enzymatic activity through elimination by evaporation of water from the surface of the fish muscle, either by exposure to the sun and wind or using various equipment [9; 81; 82; 83]. It is not recommended for fatty species due to the tendency towards lipid rancidity, which is the most important route of alteration. Prolonged exposure to the sun causes lipid oxidation, reducing its nutritional quality [68]. This method can be combined with salting, reaching a final product humidity of 15 to 20%. An ideal drying temperature of between 35 \({}^{\circ}\)C and 40 \({}^{\circ}\)C has been estimated, in addition to the fact that the process is influenced by factors such as temperature, humidity, air flow speed, and the size and thickness of the fillet [83]. Salting  
The application of salt to fish can be performed by itself or along with drying, smoke or vinegar to improve preservation and achieve sensory characteristics [60]. This method generates dehydration of the food and reduces water activity, inhibiting microbial growth due to a cellular osmotic imbalance [83, 84]. Concentrations of 6% inhibit microbial growth, and autolysis above 9% generates denaturation in muscle proteins [82, 83]. A high concentration of salt in muscle favors the loss of soluble proteins and a reduction in water retention capacity [68]. Factors such as the fish or fillet thickness, degree of freshness, fat content, salt purity, salt particle size, temperature, and hygiene during handling influence the salting process and speed of salt absorption [69, 82, 83, 85]. Salt can be generally used through a dry means for lean species in a proportion of 8 to 30% according to the region, climate, and final product characteristic, and through a wet means for fatty species [61, 69, 74, 82, 84]. Smoked  
This method consists of the application of non-resinous wood smoke where the color, smell, and flavor of the fish are modified while partial dehydration of the fish tissues occurs and its texture is modified [60, 74]. It can be used after salting and drying. The dehydration and reduction in water activity of the tissues and the presence in the smoke of compounds (phenols, organic acids, esters, and polycyclic aromatics) with antimicrobial and antioxidant activity determine the increase in the useful life of the fish, but are insufficient to allow its preservation at room temperature, so these products must be preserved through refrigeration [60, 84]. Smoking can be hot when exposed to the action of smoke at temperatures between 60 and 120 \({}^{\circ}\)C or cold at temperatures below 60 \({}^{\circ}\)C [69, 78]. Despite the benefits of smoking, it has been pointed out that lipid oxidation, protein denaturation and non-enzymatic browning reactions are the main factors responsible for these changes in the nutritional quality of these products [68, 77], specifically in the availability of lysine where its loss is proportional to the temperature and duration of smoking [68]. Once smoking is completed, the product must be stored in refrigerated conditions with a shelf life of approximately 30 days [69]. Pickled  
Pickling is performed through the combined action of salt and vinegar. The medium is acidified and the decrease in available water manages to increase the fish's useful life by slowing down microbial and enzymatic action [60, 74]. The added salt contributes to the stability of the pickle and reduces the softening action of the acid. The product is characterized by its strong flavor and smell that can be accentuated by the addition of different spices, and refrigeration is also required to preserve these products [60, 74]. Vacuum packaging is performed by removing air from inside the food packaging to protect the food from environmental contaminants and extend its shelf life.