Growth,moult and filtering rate of krill in laboratory conditions

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Experiments on moult frequency, growth, filtering and ingestion rates, and size selection of food particles were conducted in the Antarctic krill, Euphausia superba. The intermoult period ranged from 14 to 28 days, with a slight tendency that it was longer for larger specimens than for smaller ones. The dry weight proportion of the exuvium to the body varied between 4.7 and 14.1%. Carbon and nitrogen contents in the exuviae were 10.50±3.22 and 1.84±0.69% of the dry weight, respectively. During the rearing experiments, some krill clearly showed an increase in body length, but some showed a decrease. The most rapid growth is expressed by the regression equation y=0.0116x+5.88 (y : carapace length in mm, x : time in days). Growth rate expressed as an increase in body length per month was 4.5% for krill of 25mm in length. The filtering rate increased with the increase in body dry weight, while the filtering rate per unit dry weight decreased. The filtering rates at high phytoplankton concentrations were much higher than at low concentrations. Krill ingested phytoplankton by active filter feeding when it was plentiful. If phytoplankton was scarce, the filter feeding became inactive. In this case, krill cannot compensate for their metabolic loss and thus depend on predatory feeding. Krill ingested food particles larger than 8μm through their filter feeding when the particles were composed of various sizes, but they can also take minute particles less than 8μm when the majority of particles in medium were smaller than 8μm.
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Growth,moult and filtering rate of krill in laboratory conditions

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