Wednesday, January 20, 2010

Live feed in Fisheries

Manual on the production and use of live food in aquaculture.
FAO Technical Paper No. 361

Silicate is specifically used for the growth of diatoms which utilize this compound for production of an external shell. Micronutrients consist of various trace metals and the vitamins thiamin (B1), cyanocobalamin (B12) and sometimes biotin. Two enrichment media that have been used extensively and are suitable for the growth of most algae are the Walne medium (Table 2.3.) and the Guillard's F/2 medium (Table 2.4.). Various specific recipes for algal culture media are described by Vonshak (1986). Commercially available nutrient solutions may reduce preparation labour. The complexity and cost of the above culture media often excludes their use for large-scale culture operations.

Nualgi is the solution to the use of Walne medium or Guillard's F/2 medium.
Its commercially available and is economical and easy to use even in large ponds and lakes.

Wednesday, January 13, 2010

Diatom Algae in China

Shenzhen local newsper makes a featured report about Prof Jawkai Wang's project to use Diatom Algae for bioremediation of lakes and for biodiesel.

Important facts in the report:

1. The government of Kunming city, Yunnan province reached an agreement with Wang’s company to start the polution treatment project of Dianchi lake this year. At present, the government of Kunming city plans to fund 1.5 million yuan and will give another 18 million yuan six months later when the feasibility report is finished.

2. After the project in Dianchi lake, he will probably take part in the polution treatment of Taihu laike.

3. He explained to the reporter about the principles of pollution treatment with microalgae as follows:

“The reason why waters are polluted is because there too many organic nitrogen, phosphorus etc in the lake, which are in fact “fertilizers”. By using controllable algae to eat up these fertilizers, the waters can be cleaned. Conventional open-pond cultivation of algae is liable to invasion of foreign algae species, resulting in secondary pollution. Through accurate control of the nutritional salts in the waters, especially dissolvable silica, the grow rate of diatoms can be maximized so that diatoms are significantly predominant over other foreign algae species, making the diatom culturing fluid less susceptible to pollution from foreign algae species.

4. He estimates that the dry algae yield in his project will reach 270 tons per hectare per year based on his maximum daily yield, as compared to the conventional yield of only 10-20 tons per hectare per year. And the oil content in the diatom will be up to 24%.

Sunday, January 3, 2010

Cyanobacteria abundance and its relationship to water quality in the Mid-Cross River floodplain, Nigeria

Cyanobacteria abundance and its relationship to water quality in the Mid-Cross River floodplain, Nigeria
Okogwu Okechukwu I.1 & Ugwumba Alex O.2

Cyanobacteria abundance was fairly high between seasons and stations. This may be attributed to the presence of still waters in the several ponds and lakes within the Cross River floodplain with conditions conducive for the proliferation of these plankton groups. Still blackwater was suggested by del Giorgio et al. (1992) to be the likely sources of cyanobacteria bloom in rivers. In line with this, cyanobacteria abundance was remarkably higher in the lakes than in the open water. High cyanobacteria abundance in the lake was mainly attributed to crustacean grazing activities, which depleted the smaller edible algae to the advantage of the cyanobacteria (Okogwu 2008). Cyanobacteria are known to be less palatable and less attractive to zooplankton (especially cladocerans), so they receive little grazing attention (Relevante and Gilmartin 1982, Repka 1996). In cladoceran dominated lakes, cyanobacteria are known to have high densities as the grazing activities of this group of zooplankton effectively eliminate other competing alga from the phytoplankton community. This may explain the higher density of cyanobacteria recorded during the wet season compared to the dry season in most of the stations as cladoceran density attained peak in these lakes during the wet season (Okogwu 2008). The density of green algae and diatom was reported to be very low during this period (wet season) (Okogwu 2008). Grazing zooplankton remove their natural competitors (small alga) releasing nutrients to them (Repka 1996). However cyanobacteria are generally harmful to zooplankton by clogging their feeding apparatus, toxin production and poor nutritional quality of the cells (DeMott et al. 2001, Sterner and Elser 2002, Jang et al. 2003). Therefore, the cyanobacteria abundance recorded in the floodplains of the Cross River should be of concern as these are the breeding grounds of the important fishes of the river notably Chrysichthys nigroditatus, Clarias gariepinus Oreochromis niloticus and Tilapia zilli during the wet season. Fish larvae exposed to cyanobacterial toxin showed reduced feeding and growth rate (Baganz et al. 1998).

Saturday, January 2, 2010

Algal Blooms - definition - 40 ppb of Chlorophyll a

Indicator 2.3 - Lake Okeechobee Algal Blooms

What is the desired restoration condition?

The desired restoration condition for Lake Okeechobee algal blooms is to substantially reduce the frequency of blue-green algal blooms in the pelagic (open water) region of the lake. Algal blooms are defined as chlorophyll a concentrations in excess of 40 parts per billion (ppb), and the numeric goal is to reduce the occurrence of such concentrations to less than 5 percent of water samples collected in the pelagic zone (as a five-year running average). Chlorophyll a is the green pigment found in algal cells that allows them to carry out photosynthesis. It is a reliable measure of the biomass of algae in the water. A concentration of 40 ppb is used by the State of Florida and other states as an indicator of a bloom. When water has 40 ppb of chlorophyll a, it is visibly green. The scientific basis for the 5 percent goal is provided in Havens and Walker (2002).

Hydrological Alterations and Marine Biogeochemistry: A Silicate Issue?

Hydrological Alterations and Marine Biogeochemistry: A Silicate Issue?
Venugopalan Ittekkot, Christoph Humborg and Petra Schäfer
BioScience, Vol. 50, No. 9, Hydrological Alterations (Sep., 2000), pp. 776-782
(article consists of 7 pages)
Published by: American Institute of Biological Sciences
Stable URL:

Silicon Retention in River Basins

Silicon Retention in River Basins: Far-Reaching Effects on Biogeochemistry and Aquatic Food Webs in Coastal Marine Environments

Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot

Ambio, Vol. 29, No. 1 (Feb., 2000), pp. 45-50
(article consists of 6 pages)

Published by: Allen Press on behalf of Royal Swedish Academy of Sciences
Stable URL:

Silicon Retention in River Basins: Far-Reaching Effects on Biogeochemistry and Aquatic Food Webs in Coastal Marine Environments, by Christoph Humborg, Daniel J. Conley, Lars Rahm, Fredrik Wulff, Adriana Cociasu and Venugopalan Ittekkot © 2000 Royal Swedish Academy of Sciences.


Regulation of rivers by damming as well as eutrophication in river basins has substantially reduced dissolved silicon (DSi) loads to the Black Sea and the Baltic Sea.

Whereas removal of N and P in lakes and reservoirs can be compensated for by anthropogenic inputs in the drainage basins, no such compensation occurs for DSi.
[ except for Nualgi ]

The resulting changes in the nutrient composition (DSi:N:P ratio) of river discharges seem to be responsible for dramatic shifts in phytoplankton species composition in the Black Sea.

In the Baltic Sea, DSi concentrations and the DSi:N ratio have been decreasing since the end of the 1960s, and there are indications that the proportion of diatoms in the spring bloom has decreased while flagellates have increased.

The effects on coastal biogeochemical cycles and food web structure observed in the Black Sea and the Baltic Sea may be far reaching, because it appears that the reductions in DSi delivery by rivers are probably occurring worldwide with the ever increasing construction of dams for flow regulation.