Chapter one

Introduction

1.1    Background of study

The importance of aquaculture has gained momentum in many countries, especially those whose economies rely mainly on food export.The demand for fish in Nigeria mostly outstrips the local production. Nigeria is the largestfish consumer in Africa and among the largest fish consumers in the world with over 1.5millions tons of fish consumed annually. Yet, Nigeria imports over 900,000 metric tons of fishwhile its domestic catch is estimated at 450,000metric tons/year.

Aquaculture is the farming of aquatic organisms and plants in fresh, brackish or salt water. Awide variety of aquatic organisms are produced through aquaculture. These include: fishes,crustaceans, molluscs, algae, and aquatic plants. Unlike capture fisheries, aquaculturerequires deliberate human intervention in the organisms' productivity which results in yieldsthat exceed those from the natural environment alone. Such interventions are stocking waterwith seed (fingerlings), fertilizing the water, feeding the organisms, and maintaining waterquality.

The successful operation of a farm or hatchery is attributed to the key knowledge and technical applications such as: aquaculture engineering, biotechnology, water and soil chemistry, fish physiology, disease management etc. Among these, larviculture has taken priority in the industry.

Naturally, fishes in the wild depend on plankton for the survival of their hatchlings throughout their fry growing seasons. Some zooplankton are essentially used to feed fry of fish species that do not accept artificial feeds (Bryant &Matty, 1980). Arrhenius and Hanson (1993) reported that some fish species feed exclusively on zooplankton during their entire life while about 90% foods of herring (Clupeaharengus) consist of zooplankton. Sipauba-Tavares and Bachion (2002) reported that zooplankton reproduction and growth rate increases availability of better food quality for subsequent trophic levels.

Zooplankton, which most fry depend naturally upon as their live food, depends on phytoplankton that constitutes the major primary producer in the aquatic food web. Many species of live food organisms used in larviculture have superior and natural nutritional value than formulated diets. However, some live food zooplankton are selected as food sources in larviculture based on certain qualities such as purity, availability, acceptance, nutritional indicators (digestibility and organism nutrients/ energy), easily availability, easy reproduction and economically viability (Watanabe &Kiron, 1994).

Normally, fish fry grow in the wild where preys are readily available. In the hatcheries, where most of the activities are artificial, the survival of fry depends on availability of right food. Fry requires high protein food (42.0% and 52% for omnivorous and carnivorous fish respectively) for survival and growth (Tacon, 1990). It is important to note that not all zooplankton are suitable for fry rearing but live Rotifer, Moinaand Daphnia species are reported to be good freshwater zooplankton that can enhance protein and other food content for the rearing of fry in our hatcheries Olojoet al.(2003).

1.2    Statement of problem

Freshwater cat fish fry survive on freshwater zooplankton in the wild without the use of shell free artemia, or artemianauplii. This denotes that freshwater fish fry do live on freshwater zooplankton. In Nigeria, most hatcheries depend only on artemia shell free for feeding of fry throughout the early stage of development. Sometimes artemia is not accessible and if available may not be in enough quantity, or may be found only in the cities where the local farmers rarely get access to them. Often times, the artemia shell free (artificial feed) develops waste materials that pollute the water of fry culture. Owing to this limitation. In most cases, due to frustration as a result of poor survival rate of fishfry, many interested fish farmers have to change fromfingerling production to other fish in their hatcheries.

The development of freshwater zooplankton (moina) as alternative to the artemia shell free for feeding fry may help the farmers immensely in rural and even in urban areas. The use of freshwater live food zooplankton to enhance production of fishfry in our local hatcheries seems inevitable in the drive for food sustainability for human race.

1.3    Justification of the study

Many hatcheries built in Nigeria were for purposes of seeds production, genetic improvement and reducing pressure on wild fry but it’s unfortunate that there are no sufficient fry for fingerlings production. The survival of fry of planktivorous fishes that do not accept formulated diet is extremely difficult. When the yolk is exhausted, the fry starves to death as they habitually refuse inert diets.

In the culture of zooplankton through direct fertilization by Tech (1981), it was described that some dominant species may be undesirable and sometimes larger than the mouth parts of fry. In some instances where the ponds are naturally fertilized, dominant species (e.g. adult Cyclops) may be too big  for the mouth parts of the fish hatchlings and some of the organisms terrorize fry while some, such as copepods even prey on fish fry. In some cases, zooplankton may be present in the pond but not enough to meet the nutritional needs of the fry or sustain the fry.

Direct fertilization of ponds with organic or inorganic manure methods for zooplankton production always cause heavy algal bloom which may initiate deleterious water quality that could lead to high mortality of fry in such ponds.

Since the collection of zooplankton from the wild is a game of chance and seasonal, it encourages predation and disease infections on fry, this research work intends to culture monospecific culture of freshwater live food zooplankton to meet the demands of  fry production.

To provide information on how to feed them to the fish fry based on size, acceptance, and nutrient requirements for high survival rate and growth of the fish fry.The production of the live food organisms are intended to serve as alternatives to artemia shell free and Artemianauplii which are costly and not readily available locally, even if they were available they were too costly for the local farmers to avoid.

1.4    AIMS OF THE STUDY

The aims of the study are:

     i.        To determine best combination of manure and the duration of culture mono specific  local strain of moinamicurura

    ii.        To screen, isolate and culture mono specific strain of freshwater Moina live food zooplankton from the wild.

   iii.        To determine the effect of filtrate of combination manure production of  cultured freshwater zooplankton (Moina)

1.5    SCOPE AND LIMITATION OF THE STUDY

This research work intends to investigate screen live food freshwater zooplankton (Moina) that are found in our local freshwater, culture and manipulation of their population density by the use of organic and inorganic substances as manures suspension for mass production in batch culture system. The choice of shatchlings was considered because they are highly carnivorous even from fry stage of life.