Rotifer harvesting

As rotifers are the first feed of fish/shrimp larvae, their bacterial load can have a major impact on their survival (Benavente and Gatesoupe, 1988). This has led to studies on the reduction of the number of bacteria after the rotifer harvest. Munro et al (1999) found that UV light could reduce the bacterial load by more the 90 % after 2 min exposure. Suantika et al (2001) used ozone in a recirculation system to reduce bacteria densities in the rotifer culture. However, in both studies there was no effect on the microbial composition. Tanasomwang and Muroga (1992) found that sodium nifurstyrenate could lower the bacterial load by 10-100 times, while the bacterial community shifted towards fewer Vibrio and more Pseudomonas and/or Moraxella. Takaoka et al (2011) were able to reduce... 

Abstract This chapter provides an update on the most common zooplankton Uve feed species used in hatchery rearing of fish and shellfish larvae, namely rotifers, Artemia and copepods. Each section starts with a summary of the biology and ecology of these species. An overview of the most common techniques to culture, feed, harvest, disinfect and preserve these organisms is provided. Special attention is given to nutritional and microbiological aspects. Furthermore, new trends and developments are discussed. 

From a set up point of view, there are two main ways to culture rotifers in large scale that are important for hatcheries batch culture and recirculation culture. From a culture management point of view, all rotifers from a culture can be harvested in one time or a portion of the cultured rotifers can be harvested frequently (e.g. daily). 

Because the rotifer production decreases due to low water quality in batch cultures, the use of RAS to culture rotifers has been studied (Suantika et al, 2000). These culture systems allow for a higher rotifer density and higher reproduction rate. The rotifer culture can be maintained for a longer period (e.g. several weeks). As a consequence, hatcheries can run smaller scale systems and produce rotifers at a cheaper cost compared to batch cultures (Suantika et al, 2003). Most of the time, these culture systems are operated in a semi-continuous manner. As soon as the rotifer density surpasses a given density, part of the culture is harvested and part of the water is replaced (Suantika et al, 2003). 

A rotifer culture can be harvested all at once or partially (see above). As the rotifer culture water has high organic loads (rotifer feed, dead rotifers. 

The microbial community of the rotifers can also be shifted through a microbial enrichment (Makridis et al, 2000). This enrichment takes place after the rotifers have been harvested and prior to feeding them to the predator larvae. Makridis et al (2000) harvested and rinsed rotifers and exposed them to 5 x 10 CFU/mL of four probiotic species for 20-60 min. The probiotics remained associated with the rotifers for 4-24 h when placed in tanks with Tetraselmis sp. mimicking the conditions in turbot larvae tanks. 

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