Moulting and body shrinkage in the Antarctic krill, Euphausia superba

Full description

Euphausia superba were collected from the Antarctic Ocean during the cruise by RV Kaiyo-Maru in January 1980, and were transported to the Australian Institute of Marine Science laboratories at Townsville in February 1980.Specimens of Euphausia superba were maintained in a cold room at -0.5°C (0 to -1.0°C) under continuous subdued light (Specimens were checked daily for moults, which were then preserved with a few drops of buffered formalin (40%) in seawater. The exopodite length of the moult uropod was later measured. Changes in body wet weight or length were then tracked by applying allometric equations derived from specimens sacrificed at the end of experiments. Preserved moults were later rinsed in distilled water to remove formalin and salts, and were dried in a desiccator over silica gel at room temperature to obtain dry weights. Fresh moults, collected from stock specimens were used for analysis of carbon and nitrogen using a elemental analyser (Perkin Elmer, model 240) with acetanilide as standard.In another experiment, conducted over a period of 211 days, using the same temperature, light and seawater conditions described above, 15 Euphausia superba of various sizes were maintained individually in sea water filtered through a HA Millipore filter, 0.45µm pore size (starved). Two control groups of 15 individuals each were fed, ad libitum, an artificial pet fish food (Tetra Marin) and frozen copepods (Calanus finmarchicus) or a mixture of microalgae (Dunaliella tertiolecta and Phaeodactylum tricornutum). During the experiment, handling of specimens was minimised to avoid possible damage. Changes in body wet weight were tracked as described above.At the end of the experiment, physiological rates (oxygen uptake, ammonia excretion, inorganic phosphate excretion, dissolved organic nitrogen (DON) excretion, dissolved organic phosphate (DOP) excretion) were measured by a water bottle method, where individual specimens were placed into 250 to 1000 ml glass bottles filled with the filtered sea water for 24 h in the dark at -0.5°C. Dissolved oxygen, ammonia, and inorganic phosphate were measured by Winkler titration, phenolhypochlorite, and molybdate methods, respectively. DON and DOP were determined by a UV irradiation method.The individuals were weighed (wet weight) and freeze-dried for the determination of dry weight and analyses of elemental composition (C, N, P). The analyses of C and N were made with an elemental analyzer (Perkin Ebner, Model 240) using acetanilide as standard. Determination of P was made by the molybdate method after digestion of samples in 50% (v/v) H2SO4 for 1 hour at ~ 100°C followed by neutralization with KOH.
Laboratory experiments were undertaken to examine the relationship between different feeding regimes and/or body sizes and moulting in the krill, Euphausia superba. Experiments were also carried out to determine whether cessation of feeding could be a possible over-wintering mechanism for this species.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The exopodite length (x mm) was converted to the body length (the tip of rostrum to the distal end of telson, yL, mm) or body weight (wet weight, yW, mg) by using the following equations:yL=2.646+7.360x (r=0.980,n=67)andlogyW=-2.614+2.885logx (r=0.986,n=23)These relationships were established on preserved and fresh specimens of Euphausia superba of various sizes, respectively.The water bottle method used to collect samples for determination of rates of oxygen uptake, ammonia excretion, inorganic phosphate excretion, dissolved organic nitrogen (DON) excretion, dissolved organic phosphate (DOP) excretion is described in: Ikeda, T (1974) Nutritional ecology of marine zooplankton. Mem. Fac. Fish., Hokkaido Univ., Vol. 22, pp. 1-97.The methods used for the determination of dissolved oxygen, ammonia, inorganic phosphate, DON and DOP are described in:Strickland, JDH and Parsons, TR (1972) A practical handbook of seawater analysis. Bull. Fish. Res. Board Can., No. 167, 310 pp.

Notes

Credit
Ikeda, Tsutomu, Dr (Principal Investigator)