The effects of plankton on Tilapia growth using organic and inorganic fertilizers and what causes phytoplankton bloom to
Introduction 4-5 Literature review 6-16 Objective of experiment 17 Materials 18
Plankton is also one of the main sources of food for fish. They are the most common prey for all fish larvae. Plankton has its place in the lower regions of the food chain and is the basic source of food for small aquatic animals like fish larvae. During the early stage of their life cycle fish rely on their yolk sac for nutrition. They also rely on plankton to survive during its development stage. And if the number of plankton decreases, the population of fishes will be greatly affected. This cycle clearly demonstrates the impact of plankton upon pond life. Fish farmers have increased fish yields in ponds by using inorganic or chemical fertilizers and organic fertilizers or "manures." (Bocek, 2009)
When ponds are fertilized with organic and inorganic fertilizers, nutrients stimulate the growth of microscopic plants in the water (phytoplankton). Phytoplankton is food for other organisms (zooplankton and larger animals) that are eaten by fish. Abundant growth of these microscopic plants gives water a turbid, greenish color (called a “bloom”) that can prevent light from
reaching the pond bottom and reduce the growth of rooted aquatic weeds. Fish farmers and recreational farm pond owners fertilize ponds to increase fish. Aquaculture ponds are fertilized to increase the available natural food (phytoplankton and zooplankton) for fry or larval fish, or for species that are efficient filter feeders.
Some ponds have very dense algae blooms dominated by one or two species. For reasons that are not well understood, these blooms are subject to spectacular collapse, often called a “crash,” where all the algae suddenly die. This research would highlight the effects of plankton on Tilapia growth using organic and inorganic fertilizers and the causes of phytoplankton blooms to “crashes.”
It was found that when organic fertilizers are used there is a higher phytoplankton bloom and higher oxygen level in the tanks where as when inorganic fertilizers are used there is a greater zooplankton population.
When organic and inorganic fertilizers are combined it provides food for fishes and the fishes in the combined tank had the highest weight gained.
Brachionuspala and Daphnia pulex which are plankton-feeding animals, will decrease the
numbers of the phytoplanktonvery rapidlywhenpresent in high numbers.
A fishpond is a unique environment created by man. It must be managed properly to achieve good fish production. For centuries fish farmers have increased fish yields in ponds by using inorganic or chemical fertilizers and organic fertilizers or "manures." (Bocek, 2009)
The major objective of applying fertilizers in fishponds is to enhance the primary productivity of the fish ponds i.e. to assure abundance of different fish food organisms (mainly phytoplankton, benthos and periphyton) in the aquatic environment. This encourages growth and production of fishes which feed on these organisms. Improved primary productivity in a fish pond requires adequate space, moisture, light, nutrients, favorable pH, temperature and absence of toxic substances. Of these, considerable importance has been laid on the influence of nutrient concentrations of pond environment on primary productivity. Other factors remaining favorable, nutrient concentrations determine the magnitude of phytoplankton growth, which relates to total fish production. Hence for obtaining maximum fish production, it is necessary to maintain the nutrient status of the pond to an optimum range. (Brunson et al, 1999). A well-managed fertilized recreational pond can produce 200 to 400 pounds of fish per acre annually. This is three to four times the fish production that can be obtained without fertilization.
Phytoplanktons are free-floating microscopic algae. Photosynthetic activity by large plankton populations can produce enough oxygen to cause oxygen super saturation of water during mid-afternoon on bright sunlit days.
Phytoplankton growth is stimulated by addition of nitrogen, phosphorous and potassium. Populations may "bloom" 7 to 10 days after large inputs of nutrients, or "crash" when nutrients are depleted, or if toxic chemicals are added to the water. Phytoplankton respiration may be nearly 80% of oxygen consumption in water, and respiration by large phytoplankton populations may deplete oxygen in ponds during sustained periods of cloudy weather or at night.
There are two main sources of algal species used in aquaculture. These are: (1) natural populations of phytoplankton, either as they are found in nature or from cultures enriched by adding nutrients and (2) unialgal cultures. Unialgal cultures are essential when a high quality feed source with known nutritional properties is required.
Most species are unicellular or filamentous freshwater forms. The best known algae, such as Chlorella, Chlamydomonas, Dunaliella and Haematococcus, belong to this group. Some species accumulate high concentrations of carotenoids under certain culture conditions. Chlorella is spherical in shape, about 2 to 10 μm in diameter, and is without flagella. Chlorella
contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. Through photosynthesis it multiplies rapidly requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce.
The natural productivity of a fish culture system depends largely on the availability of natural food organisms and on favorable environmental conditions for the fish.
Phytoplankton, the floating microscopic plants that give water its green color, are the first step in the food chain of fish ponds. Other organisms also feed on them and multiply, increasing the availability of natural food for fish stocked in the pond. In addition to carbon dioxide (C0) , 2
water and sunlight for carbohydrate synthesis, phytoplankton need mineral elements including nitrogen, phosphorus, potassium, calcium, sulfur, iron, manganese, copper and zinc for their growth and nutrition. To promote phytoplankton growth and maintain the optimum natural productivity of ponds, the water must contain adequate amounts of these nutrients. What are Fertilizers?
Fertilizers are natural or synthetic substances that are used in ponds to increase the production of
the natural food organisms to be eaten by the fish. These organisms include phytoplankton,
zooplankton and insects they are all part of a complex food web converging toward fish
production. By increasing the availability of major nutrients, fertilizers promote the development of
plank tonic algae, which provide food for many fish. Fertilization also leads to the development of
animals which feed on algae, including some fish such as the Chinese silver carp and the Nile tilapia. (See Annex I)
When a fertilizer is added to a fish pond, the chemicals it contains dissolve in the water, where a
portion is usually rapidly taken up by the phytoplankton present, either to be stored, sometimes in
quite large proportions, or to be assimilated and used for growth, reproduction, etc.;
Another portion is attracted by and becomes attached to the organic and mineral particles present,
both in the pond water and in the upper layers of the bottom mud or soil. This second portion may also assist the development of bacteria, responsible for the
decomposition of organic matter. The decomposition of organic matter may in turn release more nutrients back into the mud or water. The chemicals attached to soil particles may also later be released back into the water slowly, over a long period of time. They may also migrate
deeper into mud and soil, where they will no longer affect the water body, unless the pond bottom is dried or ploughed.
Most of these phenomena are linked with and controlled by water quality and in particular
temperature, pH, alkalinity and dissolved oxygen level. (Brunson et al, 1999) Types of Fertilizers
Brunson, (1999) indicated that pond fertilizers form two distinct groups: mineral or inorganic
fertilizers, which contain only mineral nutrients and no organic matter; they are manufactured industrially to be used in agriculture for improving crop production and they can be obtained from specialized suppliers.
Organic fertilizers, contains a mixture of organic matter and mineral nutrients; which are produced locally, for example as wastes from farm animals or as agricultural wastes. The formulation of a fertilizer tells the percent by weight of nitrogen (N), phosphorus (as PO), 25
and potassium (as KO) in the fertilizer. For example, an 11-37-0 fertilizer contains 11 percent 2
nitrogen, 37 percent phosphorus (as PO), and 0 percent potassium (as KO). Phosphorus is the 252
most important nutrient in ponds, but nitrogen and potassium may be needed occasionally. In new ponds, some nitrogen may be beneficial, while potassium is rarely, if ever, needed. Organic materials are not recommended for fertilizing recreational farm ponds, as excessive amounts may lower dissolved oxygen to a critical level, possibly killing fish. The fertilizers can promote the growth of undesirable filamentous algae (commonly known as “Blue green algae”, “pond moss” or “pond scum”). Fertilizers are available through any farm supply dealer and are formulated specifically for ponds, but any fertilizer formulation with the appropriate nutrient levels can be used unless the product contains other ingredients that may be harmful to fish or other aquatic organisms. For example, do not Use fertilizers intended for lawn or turf application that contain either herbicides or insecticides. (Brunson et al, 1999) WHY FERTILIZE PONDS?
Microscopic green plants called algae or "phytoplankton" form the base of the food chain for fish. All green plants need proper temperature, light, and nutrients for growth. If sufficient light and proper temperature are present, the nutrients in chemical fertilizers (nitrogen, phosphorous and potassium) are readily assimilated by phytoplankton and their abundance increases. Manure contains the same nutrients which are released and become available to phytoplankton during and after decomposition. As phytoplankton assimilate fertilizer nutrients and reproduce to form dense communities’ pond water turns a greenish or brownish color. This is called a phytoplankton bloom.
Sudden death of phytoplankton or algal bloom, "bloom crash", may result from insufficient
light (e.g. cloud cover) for photosynthesis, inadequate pond nutrients (a bloom too dense to be
supported by available nutrients and oxygen) and/or bloom senescence (the plant cell line becomes too old to continue reproduction). Oxygen is consumed or depleted when dead phytoplankton/algae decay. During the nighttime hours, a dense phytoplankton bloom can remove all oxygen from the water for respiration (to breathe) alone. When a bloom crash occurs, the water appears to have become "black" or clear overnight.
Another phenomenon is where the culture gradually loses the colour over a couple of days, whereby something is eating all the phytoplankton; under close inspection there is a burgeoning population of rotifers and cladoceras.
As phytoplankton multiply they are eaten directly by some fish or by other mostly microscopic aquatic animals called "zooplankton." Phytoplankton and zooplankton (collectively called "plankton") also serve as food for larger aquatic organisms. Through a complexed chain of interactions, fertilizers increase production of natural food organisms eaten by fish. Different fish may have different food preferences. Some can filter plankton, others eat aquatic insects and others may feed on decomposing material. See figure 1. (Bocek, 2009)