Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: October 7, 2004
Publication Date: January 17, 2005
Citation: Green, B.W., Perschbacher, P., Ludwig, G.M. 2005. Impact of threadfin shad on plankton in channel catfish production ponds. Book of Abstracts, Aquaculture America. p. 159.
Interpretive Summary: Summary Not Required.
The impact of threadfin shad on phytoplankton and zooplankton populations was studied in ponds where channel catfish (Ictalurus punctatus) are fed daily or every third day, using a 2 x 2 factorial design, where the factors tested were presence/absence of threadfin shad and feeding frequency of daily or every third day. Pre-spawn adult threadfin shad were stocked at 408 kg/ha into ponds. Each pond then was stocked with stocker channel catfish (5,040 kg/ha) and fingerling catfish (14,820/ha).
Mean chlorophyll a concentration in ponds fed daily was 194.4 mg/m3 where shad were stocked, lower (p = 0.058) than the 319.9 mg/m3 in ponds where shad were absent. In ponds fed every third day, mean chlorophyll a concentrations were 208.5 and 154.3 mg/m3 (p = 0.336) where shad were present or absent, respectively. The number of phytoplankters in ponds with and without shad was variable and averaged 6,426 and 7,798/mL, respectively. Shad affected the phytoplankton population composition. Diatoms were significantly more prevalent in shad ponds on 5 of 15 sample dates and diatom percentages (40-74%) were highest during July, August and September. Bluegreen algae were lower by an order of magnitude in shad ponds on 8 of 15 sample dates. Bluegreen algae were high in May and June (11-56%) in ponds with shad, but declined continuously thereafter, while in ponds without shad bluegreens comprised 65-91% of algae numbers during May, August and September. Shad also affected zooplankton populations. Copepod and cladocerans numbers decreased 60-86% within a month of stocking shad and remained low throughout the experiment. Rotifer numbers were high in all ponds from April through June, and were significantly higher in ponds without shad during July through September.