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The Biological Characteristics of Organisms Involved in Blue Biotechnologies

1.1. Fish

1.1.1. Tilapia

The genus Tilapia includes some 40 species from East Africa. In the vernacular, the term "tilapia" is used to designate species belonging to the genus Tilapia and also to the genera Oreochromis and Sarotherodon. Two species are mainly exploited for human consumption: Nile tilapia (Oreochromis niloticus) (see Figure 1.1) and Mozambique tilapia (Oreochromis mossambicus). Tilapia are freshwater fish with an omnivorous diet, but with a strong herbivorous tendency.

Nile tilapia is the most consumed species and contributes to the diet of many populations on the African and Asian continents. This species, raised in Ancient Egypt, was able, after introduction, to adapt to different ecosystems far from its continent of origin (Japan, Thailand, Vietnam, Brazil, China). It is a tropical fish that lives in shallow waters and has a strong aptitude for colonizing ponds and streams. However, the Nile tilapia is very sensitive to water temperature. Temperatures below 11°C and above 42°C prove to be lethal for this organism. Water depth is also a parameter that plays a significant role in mortality (El-Sayed et al. 1996). A depth of 200-300 cm reduces mortality observed for fish living at a depth of 50 cm by approximately 50% (see Figure 1.2).

This is an important criterion, particularly for breeding this species. In addition to habitat depth, temperature has a major influence on growth (see Figure 1.3). It also plays a role in the reproductive process, since spawning, after sexual maturation, is only possible when water temperature reaches 24°C.

Figure 1.1. Oreochromis niloticus or Nile tilapia (photo credit © Tørrissen B.C. 2012, Wikimedia/CC BY-SA 3.0)

Figure 1.2. Impact of pond depth on the survival of Nile tilapia (Oreochromis niloticus) (average over 10 months of rearing) (from El-Sayed et al. (1996))

Figure 1.3. Impact of pond temperature on the specific growth rate of Nile tilapia (Oreochromis niloticus) at a depth of 3 meters (from El-Sayed et al. (1996))

1.1.2. Trout

"Trout" is the common name for several species of fish belonging to the Salmonidae group. Two distinct taxa or genera, the genus Oncorhynchus and the genus Salmo, are listed principally. A third, the genus Salvelinus, including the species Salvelinus fontinalis, known as speckled or blue trout, is included in the common trout group. The common trout found in whitewater rivers generally belong to the Salmo trutta species (see Figure 1.4). In contrast, rainbow trout, which is used worldwide in aquaculture, is listed under the scientific name of Oncorhynchus mykiss. Other trout species, or even subspecies, are also harvested or exploited in aquaculture but are more limited than the previous two species. They live in a wide variety of environments, including whitewater rivers, lakes and the marine environment (see Table 1.1). Like salmon, some trout species are anadromous. This is particularly true of rainbow trout (Oncorhynchus mykiss), which leave the marine environment to reproduce in freshwater rivers. Trout are carnivorous fish, feeding on aquatic and aerial insects and various invertebrates. Examples of cannibalism by trout towards their fry have also been reported for some species and under some conditions (Lestage 1937). This is particularly true of Salmo trutta and Salvelinus alpinus (Arctic trout) (Klemetsen et al. 2003).

Figure 1.4. Salmo trutta fario or common trout (photo credit © Engbretson E. 2006, Wikimedia/public domain)

Table 1.1. Examples of different trout species and their habitats (based on FAO (2020) and Wikipedia)

Trout species or subspecies Common name Living environment Oncorhynchus mykiss Rainbow trout or salmon Well-oxygenated seas and rivers Oncorhynchus mykiss aguabonita Golden trout High-altitude lakes and rivers (> 2,100 m) Oncorhynchus clarkii Cutthroat trout Seas (Alaska) and rivers (Northern California) Salmo trutta trutta Sea trout Seas (Atlantic and Mediterranean) Salmo trutta fario Brown trout Mountain streams, rivers, brooks Salmo trutta lacustris Silver trout Lakes Salmo trutta ferox Ferox trout Lakes (Iceland, Scotland) Salmo trutta labrax Black Sea salmon Sea (Black, Azov, Caspian and Aral seas)

1.1.3. Atlantic salmon

The term "salmon" is applied to various species belonging to the Salmonidae group. There are three main genera (Oncorhynchus, Hucho, Salmo), with varying numbers of species (see Table 1.2). The genus Salmo is represented by one species, Salmo salar (see Figure 1.5), known by its common name of Atlantic salmon. This species occurs naturally in the northern Atlantic zone and along its watershed. However, the significant development of aquaculture activity around this species has led to its presence in fish farms in the Southern Hemisphere, such as in Chile, which is one of the three main producers of Atlantic salmon, along with Norway and the United Kingdom. The genus Hucho comprises two species found mainly in the rivers of eastern Europe and the Far East (Siberia). Finally, the genus Oncorhynchus comprises eight species found in the northern part of the Pacific Ocean and its watershed. Most salmon species are anadromous, similar to some trout species (see section 1.2).

Figure 1.5. Salmo salar or Atlantic salmon (photo credit © Fjeld H.P. 2006, Wikimedia/CC BY-SA 2.5)

Some species belonging to the genus Oncorhynchus may be known by more than one common name. This is particularly true of Oncorhynchus keta, which is known by four different common names (see Table 1.2).

Salmon is a carnivorous fish that feeds on small aquatic insects and mayflies in freshwater. In the marine environment, their diet is based on the predation of various crustaceans, including shrimps rich in astaxanthin, the pigment that gives salmon its red flesh. They also feed on fry or small fish of different species. Independently of this aspect, cannibalism is also known to exist in the Salmo salar species (Klemetsen et al. 2003).

Table 1.2. Examples of species grouped under the generic name of salmon and natural geographical areas (from Wikipedia)

Salmon species Common names Natural geographical area Salmo salar Atlantic salmon North Atlantic and watershed Oncorhynchus kisutch Silver salmon
Coho salmon North Pacific and watershed Oncorhynchus keta Dog salmon
Pacific salmon
Keta salmon
Chum salmon North Pacific and watershed Oncorhynchus tshawytscha Chinook salmon King salmon North Pacific and watershed Oncorhynchus masou masou Japanese salmon Masu salmon Far East Oncorhynchus nerka Nerka salmon Red salmon North Pacific and watershed Oncorhynchus gorbuscha Pink humpback salmon North Pacific and watershed Hucho hucho Danube salmon Huchen Eastern and northern Europe

1.1.4. Carp

As before, the common name carp encompasses a number of different fish species. These belong to the Cyprinidae group. The common carp is identified by its Latin name, Cyprinus carpio. Other species with multiple common names are also listed (see Table 1.3). In particular, the name "Asian carp" covers several different species, which have in common that they live in the geographical area of the Asian continent or Eastern Siberia. Carp are freshwater fish that live in the middle and lower reaches of rivers. In addition to this habitat, the common carp is also found in the wild in flooded areas, lakes and reservoir waters. They are omnivorous fish, feeding mainly on plant debris and plants (algae), as well as on mollusks and invertebrate larvae (insects, worms and crustaceans).

Table 1.3. Some examples of species grouped under the common...