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Aquaculture 182 2000 249–260 www.elsevier.nlrlocateraqua-online
Bacterial additives that consistently enhance rotifer growth under synxenic culture conditions
1. Evaluation of commercial products and pure isolates
P.A. Douillet
The UniÕersity of Texas at Austin, Marine Science Institute, 1300 Port Street, Port Aransas, TX 78373, USA Accepted 20 July 1999
Abstract
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Axenic rotifers Brachionus plicatilis Muller were cultured under aseptic conditions; they
¨
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were fed either a bacteria-free artificial diet AD , or axenic Isochrysis galbana, or a combination of axenic Chlorella minutissima and the bacteria-free AD. The medium was inoculated with
commercial bacterial additives or cultured strains of marine bacteria. The highest improvements in Ž
. growth rate GR of rotifer populations were obtained with laboratory grown bacteria. Addition of
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an Alteromonas strain and an unidentified Gram negative strain B3 consistently enhanced rotifer GR in all experiments, and under all feeding regimes in comparison with control cultures
inoculated with microbial communities present in seawater, or maintained bacteria-free. None of the other isolates or commercial products were consistent in their enhancement of rotifer
production. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Rotifer; Brachionus plicatilis; Isochrysis galbana
1. Introduction
The rotifer Brachionus plicatilis has become a valuable and, in many cases indis- pensable, food organism for first feeding of a large variety of cultured marine finfish and
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crustacean larvae Watanabe et al., 1983; Lubzens et al., 1997 . However, suppressed
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PII: S 0 0 4 4 - 8 4 8 6 9 9 0 0 2 7 1 - 9
growth or unforeseen death of rotifers are frequently observed in mass cultures Ž
. Hirayama, 1987; Ushiro et al., 1990; Maeda and Hino, 1991; Hino, 1993 . Rotifer
cultures harbor very large bacterial populations, which have been estimated to be in the
7 y1
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order of 10 cells ml
Nicolas and Joubert, 1986; Nicolas et al., 1989 . Rapid successional processes in the microbiota have been observed during the culture of
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rotifers Maeda and Hino, 1991 , and changes in the microbial ecosystem have been Ž
. postulated as the cause of the collapse of rotifer cultures Hino, 1993 .
The effects of bacteria on rotifer cultures are strain specific, as demonstrated by the Ž
. Ž
. Ž
. findings of Yasuda and Taga 1980 , Yu et al. 1988 , Gatesoupe et al. 1989 , Maeda
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and Hino 1991 and Hagiwara et al. 1994 . These authors reported strains, from diverse taxonomical groups, that were able to either decrease or increase the growth rate
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GR of B. plicatilis. However, bacterially mediated changes in rotifer GRs are caused by diverse mechanisms. A nutritional contribution of bacteria to rotifer diets has been
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Ž demonstrated by supply of vitamin B
Yu et al., 1988 or inorganic nutrients Hessen
12
. and Andersen, 1990 . In contrast, production of bacterial toxins has been found to
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reduce rotifer survival rates Yu et al., 1990 . Another possible effect of bacteria in rotifer cultures is the biochemical transformation of accumulated waste products.
Nitrogen budgets carried out with rotifers fed Nanochloropsis sp. revealed that 82– 84 of the ingested N was released into the water as metabolic excretion and feces
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. Tanaka, 1991; Hino et al., 1997 . Accumulation of metabolic products and excess
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uneaten food cause deterioration of water quality Lubzens, 1987 , which may affect Ž
. rotifer growth and reproduction Tanaka, 1991 . In fact, rotifer densities have been
Ž reported to decrease with increases of either un-ionized ammonia Yu and Hirayama,
. Ž
. 1986 or nitrite Lubzens, 1987 . Removal of waste products from rotifer cultures has
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been reported to extend the harvest period Lubzens, 1987 . A bacterially mediated improvement in water quality might be a very plausible mechanism for increasing rotifer
GRs. In this study, the effects of additions of laboratory-grown microbes and several
commercial bacterial additives were evaluated on the GR of B. plicatilis cultured under synxenic conditions, i.e., rotifers were grown in the presence of a known number, one or
more, of microbial species. Single strains and commercial products with diverse characteristics that might be beneficial for rotifers were selected so that the evaluation of
microbes would cover different plausible bacterial mechanisms for rotifer culture
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enhancement. The screening of microbes was carried out under an artificial diet AD and different algae feeding regimes.
2. Materials and methods
