Commercially Important Fish and Shell Fish Species
The shell fish resources of waters include marine shrimps, crabs, lobsters, and oysters’ etc.. These shell fishes have proven to be very resourceful in terms of rich protein sources in the diets of man and being a good source of foreign exchange thereby enriching the economy.
Artisanal and industrial fishing activities are of great importance in our coastal and marine waters. Artisanal sector consists of small sub-sectors such as lagoon, estuarine and inshore canoe fisheries, which are characterized by low capital outlay and remains the main source of fish production in Nigeria.
The industrial sector however involves high capital outlay required to employ advance technology, purchase vessels and build cold storage etc.
Read Also: Strategies for Reducing Water Pollution
1. Shrimps and Prawns
Shrimps and pawns are used jointly in most parts of the world in a state of confusion. In most recent aquaculture study, the name prawn appears to be used for fresh water forms of Palaemonids and shrimps for the others, particularly the marine species.
Shrimps and prawns have become high-value commodities in many developing countries, including Nigeria mainly because of their export market potential.
Species of prawn (Palaemonidae) include Palaemonetes monodon, P. indicus, and P.orientalis while family Penaeidae includes species such as Panaeus orientalis, P. monodon, P. japonicus and P. setiferus.
In the present state of knowledge on shrimp nutrition, fresh food continues to be important in larval and fry rearing, as well as adult grow-out. Commercial feeds are becoming available in many areas, but their acceptance in commercial farming is rather slow. When used, many farmers supplement them with natural foods and feedstuffs.
2. Crayfishes and Crabs
Aquaculturists worldover have devoted more time for the culture of crayfishes (crawfishes), lobsters and crabs due to high market demand for them. However, it is only crayfishes that presently account for any significant production through culture and some small-scale production of crabs have also been exported from tropical countries, Nigeria exclusive.
The long time (gestation period) the juveniles take to grow to market size and pronounced cannibalism at both larva and adult stages, have made available technologies for culture uneconomical commercially.
Crayfishes belong to families Cambaridae and Astacidae and it is widely distributed over all continents including Africa. The most important species include Procambarus clarkii, Pacifastacusleniusculus, and P. acutus.
The breeding season of crayfish is around September when rising water level entices the females to release the young and become more active outside their burrows. Crayfish are omnivorous but the bulk of their diet consists of microbial-enriched detritus.
Vascular plants and epiphytes are also relished as food items while animal matters or remains such as worms, insect larva, mollusks and zooplankton are very much preferred by juvenile crayfish.
Read Also: Morphology and Basic Structures of Fisheries
Crabs belong to the family Brachyura and the common species for commercial purpose is the Pre-moult blue crabs (Callinectes sapidus) in the U.S.A. Apart from this, Japan has been the country with the widest or largest commercial production level of crab in the world. Seed stock
of the Japanese blue crab Neptunus pelagicus is regularly produced in hatcheries for stocking open waters as well as larva of Portunus trituberculatus.
Other successfully spawned species in Japan is the king crab, Paralithodes camtschatica. This stage of crab production is however not met by Nigeria aquaculture status as it is under exploited.
There are three groups of marine crabs found in Nigeria waters. They are:
(a) The estuarine species which include members of the family Gecarcinidae and Grapsidae.
(b) The swimming species in inshore waters all belonging to thefamily Portunidae.
(c) The deep sea crabs, mainly Geryonidae, which form is an important component of the benthic ecosystem on the continental shelf.
3. Oysters
Cultivated oysters belong to two genera: Crassostrea (the cupped oysters) and Ostrea (flat oysters). Though aquaculture production of cupped oysters is much higher than that of flat oysters, the latter is held in greater esteem to be served on the half-shell and command a much higher price in many countries.
The more important species being cultivated the world over are; Crassostrea gigas (Pacific oyster), C.virginica (American oyster), C. Angulate (Portuguese oyster), C.commercialis (Sydney rock oyster), C. glomerata (Auckland rock oyster), C. plicatula (Chinese oyster), C. rivularis (Chinese oyster), Ostrea edulis (European oyster), Ostrea edulis (European oyster), O.
chilensis (Chilean oyster) and Crassostrea gasar (Mangrove oyster).
Although, not yet at commercial production stage, Crassostrea gasar is found in abundance in mangrove water of Nigeria coastal swamps and have been exploited subsistently. Other bivalves that are being exploited in Nigeria include the ark clams Senilla senilis, Anadara senegalensis and Cardium costratum.
Read Also: Understanding Fish Identification Process
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