Abstract
Generally zooplankton growth is often limited by the quality of their algal diet. A cheaper common practice in aquaculture, is to culture algae with fertilizers; however, the demography of zooplankton when fed these algae has not yet been evaluated. We studied the population growth and life table demography of the rotifers Anuraeopsis fissa and Brachionus rubens, and the cladoceran Moina macrocopa. For this, the algae Scenedesmus acutus or Chlorella vulgaris were cultured on defined (Bold's basal) medium or the commercial liquid fertilizer (Bayfolan). Experiments were conducted at one algal concentration 1.0 x 10(6) cells/mL of C. vulgaris or its equivalent dry weight of 0.5 x 10(6) cells/mL of S. acutus. The population dynamics were tested at 23 +/- 1 degrees C in 100 mL transparent jars, each with 50mL of the test medium, with an initial density of 0.5indiv/mL, for a total of 48 test jars (3 zooplankton 2 algal species x 2 culture media x 4 replicates). For the life table experiments with M. macrocopa, we introduced 10 neonates (<24h old) into each test jar containing the specific algal type and concentration. For the rotifer experiments, we set 5mL tubes with one neonate each and 10 replicates for each algal species and culture medium. We found that the average rotifer life span was not influenced by the diet, but for M. macrocopa fed S. acutus cultured in Bold's medium, the average lifespan was significantly lower than with the other diets. The gross and net reproductive rates of A. fissa (ranging from 18-36 offspring per female) were significantly higher for C vulgaris cultured in Bold medium. Regardless of the culture medium, Chlorella resulted in significantly higher gross and net reproductive rates for B. rubens than S. acutus diets. The reproductive rates of M. macrocopa were significantly higher in all the tested diets except when fed with S. acutus in Bold medium. The population increase rate, derived from growth experiments of A. fissa and B. rubens, ranged from 0.1-0.25/d and were significantly higher on C vulgaris cultured in liquid fertilizer as compared to the other diets. The growth rates of M. macrocopa ranged from 0.1 to 0.38/d, and were highest with diets of C. vulgaris cultured in Bold medium and S. acutus cultured in fertilizer. Thus, regardless of the culture medium used, the growth rates of the evaluated zooplankton species were higher with Chlorella than with Scenedesmus. The peak population density was highest (2 800ind/mL) for A. fissa fed Chlorella that was cultured on liquid fertilizers, while B. rubens and M. macrocopa had peak abundances of 480 and 12ind/mL, respectively under similar conditions.
Highlights
The production of adequate amounts of live food such as zooplankton for fish larvae remains a ‘bottleneck’ in aquaculture
B. rubens cultured on the organic wastes had higher growth rate than Chlorella-fed populations; the nutritional quality of the rotifers cultured on this diet was further reflect in bioassays conducted with the predatory rotifer Asplanchna sieboldi, which had growth rates ranging from 0.05 to 0.08 per day on B. rubens cultured on C. vulgaris but 0.14 to 0.22 per day on rotifers fed organic wastes (Sarma et al 2003)
Demography: The survivorship curves of A. fissa showed a steady decline in the rate of survival with age, regardless of the diet (Fig. 1)
Summary
The production of adequate amounts of live food such as zooplankton for fish larvae remains a ‘bottleneck’ in aquaculture. Many reviews had well documented that the zooplankton requirement declines after the first 4-6 weeks, but during this period, demand is very high (50 000 rotifers per week per larva: Lubzens et al 1989). This way, aquaculture facilities have to establish economical but large scale cultures of freshwater zooplankton. The live food predominantly used in freshwater aquaculture includes rotifers and cladocerans, this is because of their adequate body size for the gape of young larvae, high growth rates and ease of maintenance. For instance, have higher lipid content at 10°C than at 25°C (Lubzens et al 1995) These factors affect the population growth of zooplankton as well as the fish larvae. In an earlier study, Kibria et al (1999) showed that the somatic growth of the perch (Perca fluviatilis) was higher on Daphnia carinata cultured in waste water than with Moina australiensis reared on the same medium
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