Common Groups of Algae in Aquaculture Ponds:
- Blue green algae
- Dinoflagellate algae
- Diatom algae
- Green algae
Blue green algae:
Blue-green algae, also known as Cyanobacteria, are a group of photosynthetic bacteria that many people refer to as “pond scum.” Blue-green algae are most often blue-green in color, but can also be blue, green, reddish-purple, or brown. Blue-green algae generally grow in ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.When a blue-green algae bloom dies off, the blue-green algae cells sink and are broken down by microbes. This breakdown process requires oxygen and can create a biological oxygen demand. Increases in biological oxygen demand result in decreases in oxygen concentration in the water, and this can adversely affect fish and other aquatic life, and can even result in fish kills.
Blue-green algal toxins are naturally produced chemical compounds that sometimes are produced inside the cells of certain species of blue-green algae. These chemicals are not produced all of the time and there is no easy way to tell when blue-green algae are producing them and when they are not. When the cells are broken open, the toxins may be released. Sometimes this occurs when the cells die off naturally and they break open as they sink and decay in a pond. Cells may also be broken open when the water is treated with chemicals meant to kill algae, and when cells are swallowed and mixed with digestive acids in the stomachs of animals.
Many different species of blue-green algae occur in waters, but the most commonly detected include Anabaena sp., Aphanizomenon sp., Microcystis sp., and Planktothrix sp. It is not always the same species that blooms in a given waterbody, and the dominant species present can change over the course of the season.
This group of algae is harmful to shrimp. Rakhoroni algae cause scum on the water surface, like Microcytis sp., it makes shrimp smell fishy and foul; it discharges gel through cell membrane, and cause blockage in shrimp’s gills.
The dinoflagellates (Greek δῖνος dinos “whirling” and Latin flagellum “whip, scourge”) are a large group of flagellate eukaryotes that constitute the phylum Dinoflagellata. Most are marine plankton, but they also are common in freshwater habitats. Their populations are distributed depending on sea surface temperature, salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy). In terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, although this group is substantially smaller than diatoms.
About 1,555 species of free-living marine dinoflagellates are currently described. Another estimate suggests about 2,000 living species, of which more than 1,700 are marine (free-living, as well as benthic) and about 220 are from fresh water. The latest estimates suggest a total of 2,294 living dinoflagellate species, which includes marine, freshwater, and parasitic dinoflagellates.
A bloom of certain dinoflagellates can result in a visible coloration of the water colloquially known as red tide, which can cause shellfish poisoning if humans eat contaminated shellfish. Some dinoflagellates also exhibit bioluminescence—primarily emitting blue-green light.
Unfortunately, a small number of species also produce potent neurotoxins that can be transferred through the food web where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish, birds, marine mammals.
Some species, such as the dinoflagellate Alexandrium tamarense produce potent toxins, which are liberated when the algae are eaten and many types of algae in this group conveying toxins that can make shrimp die.
Diatoms (diá-tom-os “cut in half”, from diá, “through” or “apart”; and the root of tém-n-ō, “I cut”.)  are a major group of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms number in the trillions: they generate about 20 percent of the oxygen produced on the planet each year; take in over 6.7 billion metric tons of silicon each year from the waters in which they live; and contribute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half mile deep on the ocean floor.
Movement in diatoms primarily occurs passively as a result of both water currents and wind-induced water turbulance; however, male gametes of centric diatoms have flagella, permitting active movement for seeking female gametes. Similarly to plants, diatoms convert light energy to chemical energy by photosynthesis, although this shared autotrophy evolved independently in both lineages. Unusually for autotrophic organisms, diatoms possess a urea cycle, a feature that they share with animals, although this cycle is used to different metabolic ends in diatoms.
Aquaculture ponds with significant levels of diatoms are desirable for shrimp production because of the diatoms’ high nutritional value, particularly for younger shrimp.
Silicon is second only to oxygen in abundance in the earth’s crust. Much sand consists of silica (silicon dioxide or SiO2), and clay minerals are hydrous aluminum silicates. Natural waters contain silicon because of the dissolution of silicate minerals with which they come in contact. For example, silicon dioxide reacts in water to form silicic acid, a weak acid that is largely unionized within the pH range of most natural waters. When calcium silicate reacts with carbon dioxide in water, the resulting dissolved substances are calcium ions, bicarbonate ions (alkalinity) and silicic acid.
Silicon concentrations in natural waters typically are reported in terms of SiO2 and usually range from 5 to 25 mg/L in freshwater bodies. The global average for silica in river water is 13.1 mg/L. Normal seawater contains 6.4 mg/L silica. A silica concentration can be converted to silicon concentration by multiplying by the factor 0.467, the proportion of silicon in SiO2.
Plants take up silicic acid from water. Silicon in higher plants is incorporated into cell walls, making stems and leaves more rigid and strong. Among the phytoplankton, diatoms have a particular need for silicon, because their frustules – the hard but porous cell walls – are composed almost entirely of silica. Depending upon the species, plants contain from less than 0.1% to as much as 10.0% silicon on a dry-weight basis. Diatoms contain the greatest amount of silicon.
The ratio of carbon:nitrogen:silicon:phosphorus in diatom cells averages 106:15:16:1. Thus, diatoms require about the same amounts of nitrogen and silicon for growth. There is evidence that nitrogen:silicon ratios above 3:1 lessen the growth rate of diatoms.
Diatoms have very short life cycles in the ponds, algae crashes and low-oxygen are major threats and brown gill problem. They easily cause water color change.
There are more than 4,000 species of green algae. Green algae may be found in marine or freshwater habitats, and some even thrive in moist soils.
The most important algal species are Chlorella, which are used as nutrient source in aquaculture production worldwide . Chlorella belongs to the green algae group and is being granted GRAS (generally recognized as safe) status.
Chlorella minutissima is a unicellular microalga without flagella recognized as an oil-rich green alga that exhibits many attractive features, such as easy cultivation, fast growth, and high levels of amino acids and polyunsaturated fatty acids (PUFA’s). These attractive characteristics make Chlorella minutissima as a potential microalga in pharmaceuticals and health foods .Falaise et al. have reviewed that Chlorella are versatile as they play important roles as antimicrobial agent’s like anti-bacterial, antifungal and antiviral activities against related diseases in aquaculture. For this end the “green water” technique is a useful tool against bacterial disease in aquaculture.
Antibacterial compounds from microalgae can be lipids or fatty acids. An anti-marine bacterial activity was demonstrated in vitro with the polyunsaturated fatty acid (PUFA) such as the PU free FA in P. tricornutum, identified as eicosapentaenoic acid .
PUFAs, such as Arachidonic acid (AA) (20:4 omega-6), eicosapentaenoic acid (EPA) (20:5 omega-3) and docosahexaenoic acid (DHA) (22:6 omega-3) are essential for the growth and survival of marine fish larvae . In fact, fish larvae have a very limit ability to synthesize PUFAs, which must be derived from zooplankton such as rotifers that consume algae . In rotifers production, microalgae could increase the DHA and EPA contents of the rotifers even with a short-term enrichment period. However, to observe more positive effects on growth and survival of fish larvae using rotifers with short term enrichment in microalgae, microalgae need also to be added as “green water”
This group contains no toxicity, usually has small size and doesn’t make shrimp smell and this types of algae in the water can greatly affect color and turbidity of aquaculture water.