## 7 Fish Processing and Preservation
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fish Compound** & **Fresh Status** & **Spoilage Status** & **References** \\ \hline \multirow{4}{*}{Skin} & Brilliant coloration & Discoloration & \\  & Transparent mucus & Opaque mucus & [9; 17; 60; 71] \\  & Non-viscous & Viscous & \\ \hline \multirow{4}{*}{Eyes} & Convex & Concave & \\  & Transparent & Milky & [9; 17; 60; 71] \\  & Brillant & Opaque & \\ \hline \multirow{4}{*}{Gills} & \multirow{4}{*}{Red-colored} & Yellowish & \\  & & Ref.-colored & Brownish & \\  & Brillant & Colorless & \\  & & Vispose & \\ \hline \multirow{4}{*}{Muscle appearance} & Firm & \multirow{4}{*}{Soft} & \\  & Elastic & Uniform colored & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \multirow{4}{*}{Odor} & \multirow{4}{*}{Fresh, ocean-like} & Rotten/rancid & \\  & & Sulfides, amines, and & \\  & & ammonia & \\ \hline \multirow{2}{*}{Internal organs} & Brillant & Autolysate & \\  & Defined & Acid odor & [9; 17] \\ \hline \multirow{2}{*}{Scales} & Firm, bright, and & Easy detachment and low & \\  & detachment resistant & firmness & [60] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristics of fresh or spoiled fish intended for human consumption. In general, the term quality refers to the appearance, freshness, or degree of spoilage of the fish. However, it also involves safety by considering the absence of pathogenic microorganisms or chemical substances. It should be noted that the term quality can be different for each individual and is a characteristic term associated with a particular product. It is usually considered that the highest quality is found in fish that is consumed in the immediate post-mortem period. However, fish in rigor mortis makes the filleting and skinning process difficult and inappropriate for smoking. Therefore, for processors, fish that has passed rigor mortis is recommended [8]. Food processing and preservation technologies address the continuous challenge of generating more durable products by minimizing the nutritional and sensory characteristics of the fresh product, contributing to its microbiological stability and extending shelf life [72]. In the processing of fishing and aquaculture products, the edible portion (fillet) is commonly separated to favor its shelf life [9; 61], also generating by-products that are discarded or used for processing, obtaining different value-added products intended for human or animal use such as fishmeal, oils, and hydrolysates, among others [72; 73]. The stages for the generic and basic processing of fish constitute sensory evaluation and selection (species and size), washing (causing reduction in microbial load), scaling, gutting, heading, and cutting according to the species, size, shape, preservation process, and consumer needs (Figure 1). Figure 1: Elemental processing diagram of fresh fish to obtain various products [9; 61; 74; 75]. In foods of aquatic origin, there are a variety of processing and preservation technologies that contribute to extending their shelf life and guaranteeing their safety so that they can be distributed and marketed in areas far from where they are produced. Food preservation methods are classified as modern (refrigeration, freezing, canning, vacuum packaging, and modified atmospheres) and traditional (salting, smoking, cooking, drying, and pickling), the latter being of basic and common use in fish, and which can be applied individually or jointly [76]. Preservation methods are generally based on the modification of biological activity's optimal conditions (enzymes and microorganisms) such as lowering the temperature (refrigeration, chilling, or icing and freezing), heat application (canning, cooking, and smoking), reduction in available water (drying, salting, and smoking), pH modification (picking), change in storage conditions, and absence or presence of oxygen or other gases (vacuum packaging or modified atmosphere) [4; 9; 60; 65; 70].