Abstract
Our knowledge of the consumption of plankton by fish is still fragmentary. Trophic links between fish and plankton are often loose because plankton is a changing assemblage of pelagic organisms of valuable nutritional value. The objectives of the study were to determine the distribution and diversity of planktons in the fish ponds. Water samples for plankton analysis were collected monthly (January-December), along with water samples used for the determination of physico-chemical parameters in 250 ml bottles in Ponds 1, 2 and 5. The freshwater sample was mixed gently and pipetted into 5 ml plankton chamber containing 2 drops of Lugol’s solution. The Lugol’s solution which served as fixative also enhanced sedimentation of the organisms and was left overnight before analyzing plankton using Zeiss inverted plankton microscope and plankton determination keys. Data was analyzed using Shannon-Weaner diversity index, species richness, means and analysis of varians (ANOVA). The results showed that the highest species richness for dry season phytoplankton value of 27 was recorded in Pond 2, with the highest Shannon-Weaner diversity index value of 0.5401 in pond 5. Merismopaedia elegans with 3,434 in pond 2 was the most abundant phytoplankton species and chlorophyceae the most dominant taxa. The rainy season zooplankton species richness values (5 in pond 2) were higher than that of the dry season (3 in pond 3) with the highest Shannon-Weaner index value of 0.3501 recorded in pond 1. The most abundant zooplankton species Asplanchna species 57 was recorded in pond 2. Significant differences (p < 0.05) was observed for phytoplankton and zooplankton species between the ponds. Physico-chemical parameters had influence on the distribution and diversity of planktons in the fish ponds.
Highlights
The aquatic environment supports various communities of living organisms
The results showed that the highest species richness for dry season phytoplankton value of 27 was recorded in Pond 2, with the highest Shannon-Weaner diversity index value of 0.5401 in pond 5
Lower dissolved oxygen values obtained during dry season could probably be due to higher temperatures during the season (Akpan & Offem, 1993a) while high levels of dissolved oxygen during the wet season could be due to lower water temperature and increased aeration due to agitation by wind in the wet season (Ochang et al, 2005)
Summary
The aquatic environment supports various communities of living organisms. They constitute the biotic load of a pond. Plankton designates the community of pelagic organisms, composed of various groups, which are in suspension in water and restricted mobility, often less than that of the water which carries (Declince, 1992). The following groups can be distinguished: picoplankton (from 0.02 to 0.2 μm) nanoplankton (from 0.2 to 2.0 μm) (Sieburth et al, 1978). Picoplankton and nanoplankton, often ignored in plankton studies can contribute significantly to primary productivity, often in excess of what their biomass would suggest (Hardy et al, 1986; Stockner & Antia 1986; Stockner, 1988)
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