I. FISH SPECIES

Some 20,500 species of fish are known to exist. The majority of these are found in tropical waters. One of the major differences between temperate and tropical fisheries is that the temperate fisheries tend to be based on single species such as cod and herring, while in many tropical fisheries the catch may include 30 or more species, all of which can be consumed fresh or in processed form. The fish curer working in the tropics may thus have to be prepared to preserve a range of species in differing size and fat content, some of which are delicate while others are more robust and less subject to damage. Since it would be impractical to consider more than a small number of fish types in this memorandum, four main groups are considered. In later chapters, where methods and techniques are discussed, it will be possible to be more specific.

The most important factors which affect the suitability of a fish for a particular process are:

(a) Size - Very small fish may be dried whole where weather conditions permit. Larger fish must always be cut so as to increase the surface area available for salt penetration, and/or moisture loss.

(b) Oil content - Fish oils oxidise readily and become rancid. Rancidity gives a bitter flavour to the product and this may be considered objectionable although some communities prefer dried fish to be slightly rancid. Fish which contain much oil do not generally make good salted and/or dried products since the oil acts as a barrier to salt penetration and moisture loss. Satisfactory products may be made by cooking and then drying, or by smoking. In cold climates, such fish are often pickled in salt. If this is attempted in a hot climate, fermentation is rapid, the flesh starts to break down and pastes or sauces result.

(c) Flesh texture - Fish in which the flesh is firm or moderately firm are relatively easily handled; they can be cut without falling apart and the dried product can be transported without breaking up. Fish which have a very soft flesh tend to tear when attempts are made to cut them? if dried products are made, these are very fragile and break up during transport. Fish which have both delicate flesh and a high fat content need especially careful treatment.

I.1. Small pelagic species

Small pelagic species include fish less than 25 cm long. Characteristically, such fish form schools or shoals so that large numbers may be taken at one time. The group includes the herring-like and sardine-like fish, which are slender and have relatively small scales and soft delicate flesh. Many species in this group have a high oil content. These fish are sometimes dried whole without salting, but the products are then fragile and break easily. In many parts of Africa, such fish are smoked and dried, the products again being fragile. It is difficult to control rancidity and unless the products can be marketed soon after processing, its value may be reduced substantially.

The small mackerels, such as the Indian chub mackerel, are also included in this group. These are sold fresh whenever possible, but they may also be boiled or salted and dried. This group also includes anchovies and anchovy-like fish of fresh waters. In Africa, these are often sundried without preliminary treatment while in Asia, products are often made by drying after boiling. The best fermented fish sauces are made from anchovies.

Good canned products may be made from sardines and mackerels, but as noted elsewhere in this memorandum, conditions in the developing countries rarely permit the profitable establishment of a small cannery.

I.2. Large pelagic species

The most important fish in this group are the tunas, some of them weighing 500 kg or more. Many other species reach a weight of 100 kg while others seldom attain 10 kg. The flesh is generally very firm and contains moderate amounts of oil. In some species, the flesh is very dark and many of these bleed heavily when cut. The skin of most species is thin.

Most of the world tuna catch is canned but substantial amounts are sold fresh. Fresh tuna is often highly priced and is not commonly used to make dried salted products. Two special cured products, Maldive fish (much in demand in Sri Lanka) and katsuobushi (which is popular in Japan) are made by a combination of cooking, smoking and drying. The smaller tunas, such as skipjack are most often used for these products.

The larger mackerels and horse mackerels, or jacks, have moderately firm flesh and a medium oil content. These are popular food fish and are best sold fresh when possible. Alternatively, good quality salted, dried or smoked products may be made. Canned products of good quality could be made from most of these species but they are not usually caught in sufficient quantity for canning.

I.3. Small demersal fish

Small demersal fish include bottom-living fish less than 25 cm long. They constitute a very diverse group including fish of very different shapes, but generally of deeper form than pelagic fish. Most have quite large hard scales and moderately firm flesh. Some, such as the catfish, are scaleless and have soft flesh. The oil content is variable but is generally less than 5% and there is less annual variation in oil content than is found in pelagic fish. The group includes many different types of sea fish such as small mullets, snappers, breams, croakers, jew fish and silver bellies, and small fresh water fish such as carps and breams.

Salted and dried products of good quality can be made from many small demersal fish, but the products fetch generally low prices. These products are useful in that they provide the lower income groups with a source of animal protein food. However, because their market prices are generally low, expensive refinements of processing are not possible. Being relatively lean and bony, these fish are not generally suitable for canning. They are also seldom used for making fermented products.

I.4. Large demersal fish

Large demersal fish also constitute a somewhat diverse group. It includes the sharks and rays as well as bony fish such as mullets, snappers, groupers, jew fish, breams and threadfins. Many of these bony fish are sold most profitably fresh when this is possible They can also be processed into excellent dried salted products when demand for the fresh product is not sufficient. These fish are not usually smoked or used for making boiled or fermented products. The sharks and rays need particularly careful handling otherwise the flesh may smell strongly of ammonia. Good salted dried products can be made out of these two species if processed carefully.

The fresh water fish in this group include tilapia, carp and catfish. In Africa, the latter are commonly smoked. They are also sometimes split or cut into pieces and dried in the sun.

Most of the bony fish have large hard scales, the flesh is moderately firm and the fat content relatively low. Few, if any, could be used for canning and for making fermented or boiled products.