Author
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Ludwig, Gerald |
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Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/27/2002 Publication Date: 10/1/2003 Citation: LUDWIG, G.M. THE EFFECTS OF INCREASING ORGANIC AND INORGANIC FERTILIZER ON WATER QUALITY, PRIMARY PRODUCTIVITY, ZOOPLANKTON, AND SUNSHINE BASS, MORONE CHRYSOPS X M SAXATILIS FINGERLING PRODUCTION.. JOURNAL OF APPLIED AQUACULTURE. 2003. v.12 (2). p.1-29. Interpretive Summary: Culture of sunshine bass (a female white bass X male striped bass hybrid) depends upon the presence of live zooplankton food during a short time just after fry are stocked into ponds. Fertilization is used to produce zooplankton. The fry must be stocked into the pond at just the right time, just as rotifers, the first and smallest zooplankton, appear. Then fry will consume them and grow large enough to escape or eat predatory copepods that appear next. It is not well known how much fertilizer is needed to produce enough zooplankton without degrading water quality and reducing fry production. This experiment used incremental levels of a previously published fertilizer regimen that used rice bran as an organic and liquid 9 27-0 NPK as an inorganic fertilizer. Pond replicates were fertilized at th horiginal recommended rate and at two, three, and four times that rate. Overall, increased concentrations of zooplankton in the higher fertilizer treatments should have increased production but potential increases were nullified by poorer water quality, thus production dropped as fertilizer was increased. The results of the experiment suggest that the original published fertilizer rate produced adequate zooplankton (particularly rotifers) with little water quality degradation until a week after the fry are stocked. However, after that time, her fertilization rates should be used to supplement prepared feed with higher concentrations of fertilizer. By the time the fry are large enough to withstand the rigors of aeration devices that could be used to counteract resultant low dissolved oxygen levels. Technical Abstract: Sunshine bass fingerling culture ponds were fertilized over a six week period with a combination of organic (rice bran at 472 kg/ha) and inorganic (liquid 9-27-0 NPK at 216.2 kg/ha) fertilizers and at two, three, and four times that rate to determine if survival and growth of fry could be improved. Shortly after fry were stocked at four days of age, one of thei first natural foods, rotifers, became progressively more abundant as fertilizer application increased. Ponds receiving increased amounts of fertilizer also had increased amounts of crustacean zooplankton: copepod nauplii, copepods, and cladocerans which also are important natural foods for sunshine bass fingerlings. Even though increased amounts of fertilizer resulted in increased concentrations of natural feed, fingerling survival decreased from a mean of 47% for the base level fertilizer treatment to 15.4% for ponds receiving four times as much fertilizer. Increased fertilizer application adversely affected water quality that probably detrimentally affected fish survival. Unionized ammonia nitrogen levels, ph and water temperatures in all treatments were at or above concentrations reportedly lethal to sunshine bass fry at or shortly after fry were stocked. Differences in levels of unionized ammonia nitrogen were correla- ted with differences in final survival. Low dissolved oxygen concentra- tions and chronic sub-lethal levels of unionized ammonia in the more highly fertilized treatments exacerbated differences in mortality among the treatments. |
