OPTIMUM LIGHT AND 



TEMPERATURE REQUIREMENTS FOR 



GYMNODINIUM SPLENDENS, A LARVAL 



FISH FOOD ORGANISM'.^ 



In recent years, it has been possible to sub- 

 stitute the marine dinoflagellate GymuodiiiiKni 

 splendens for wild natural plankton as a food 

 source for first-feeding larval anchovies, Eii- 

 graulis mordax (Lasker et al., 1970). G. spleii- 

 deiis is ideal for this larval marine fish at 

 this developmental stage because the alga's 

 size (approximately 53 ^m diameter) is similar 

 to the size I'ange of natural food particles. 

 Reasonably lengthy larval survival (up to 19 

 days) can be achieved in the laboratory by first 

 using this dinoflagellate and later supplementing 

 with veligers (Lasker et al., 1970). The alga 

 has also been used in combination with the 

 rotifer Brachionus pUcatilis as a larval food 

 source (Theilacker and McMaster, 1971). 



These developments have made possible new 

 studies of anchovy larval behavior (Hunter, 

 1972) and nutrition (Conklin, unpublished 

 data). Furthermore, the use of G. .sple7idens 

 may be of help in rearing other larval fish. 



G. splendens is easily grown in an enriched 

 seawater medium that was developed by Sweeney 

 (1951, 1954) and Sweeney and Hastings (1957). 

 The organism was first cultured with soil 

 extract in the medium (Sweeney, 1951) which 

 was later replaced with vitamin 6,2 (Sweeney, 

 1954). However, for routine culturing soil 

 extract suffices and also provides trace metals 

 and unknown organic factors. 



The dinoflagellate has been cultured at 16°C 

 and a light intensity of 60-70 footcandles 

 (Sweeney, 1951); at 20°C and 200-400 foot- 

 candles (Sweeney, 1954) and at 20 °C and 

 500 footcandles (Lasker et al., 1970). but 

 optimum physical conditions for growth were 

 not determined. Such information would be 



' Contribution from the Scripps Institution of Oceanog- 

 raphy. 



- This work was part of the STOR (Scripps Tuna 

 Oceanography Research) Program. It was supported by 

 the Oceanography Section, National Science Foundation 

 Grant No. GA-32529X and by Marine Research Com- 

 mittee (California Department of Fish and Game) 

 Grant No. M-13 to Reuben Lasker. The work was 

 performed in the Southwest Fishery Center. National 

 Marine Fisheries Service, NOAA. 



of value in setting up continuous cultures of 

 G. splendens or in further improving condi- 

 tions for mass cultures. The purpose of this 

 paper is to establish the optimum conditions 

 of light and temperature for G. sple)idens 

 culture — conditions that result in a maximum 

 growth rate. 



Materials and Methods 



Our culture of G. splendens was isolated 

 from a water sample taken from the Scripps 

 Institution pier in March 1969. It is unialgal 

 but not bacteria-free. Gymnodinium is main- 

 tained in the enriched seawater medium of 

 Sweeney and Hastings (1957) plus the Fe 

 solution of Rodhe (1948). One liter of medium 

 contains 750 ml seawater, 10 ml 0.1% EDTA 

 (disodium ethylenedinitrilo tetra-acetate), 2 ml 

 1 M KNO3, 2 ml 0.1 M K2HPO4, 20 ml of soil 

 extract (prepared by autoclaving equal weights 

 of untilled loam and glass distilled water fol- 

 lowed by filtration through Whatman^ No. 4 

 paper), 0.25 ml Rodhe Fe solution (prepared 

 by dissolving 1.33 g ferric citrate and 1.33 g 

 citric acid in 100 ml of double distilled water) 

 and 216 ml (glass) distilled water. Autoclaving 

 the medium results in a precipitate, which can 

 be avoided by sterile filtration. Stock cultures 

 of G. splendens were maintained at 500 foot- 

 candles (5,000 lux) and 21°C. 



Experimental cultures were grown in this 

 same medium. Cells were concentrated from 

 exponentially growing stock cultures by gentle 

 reverse filtration (Dodson and Thomas, 1964) 

 and inoculated into 65-ml bottles containing 

 50 ml of medium to give an initial cell count 

 of 200-500 cells/ml. 



The culture bottles were then placed in 

 temperature gradient block A of Thomas, Scot- 

 ten, and Bradshaw (1963). This apparatus 

 consisted of an aluminum block containing 

 30 holes. Prior to starting the experiment, 

 thermostatted cold water was pumped through 

 one end of the block and warm water was 

 pumped through the other end. This set up a 

 thermal gradient so that there were six rows 



■' Reference to trade names does not imply endorsement 

 by the National Marine Fisheries Service. NOAA. 



599 



