EFFECTS OF TEMPERATURE AND SALINITY ON 

 THE SURVIVAL OF WINTER FLOUNDER EMBRYOS 



Carolyn A. Rogers^ 



ABSTRACT 



A series of experiments was performed to determine the optimum temperature and salinity for 

 incubating winter flounder, Pseudopleuronectes americanus, embryos. Eggs in lots of 50 were sub- 

 jected to a 0.5 to 45% salinity range and a 3° to 14°C temperature range in a total of 67 salinity- 

 temperature combinations. Highest proportion of viable hatches occurred at 3°C over a salinity range 

 of 15 to 35%. At temperatures above 3°C, the optimal range was 15 to 25%. Viable hatch decreased with 

 increasing temperature. 



The winter flounder, Pseudopleuronectes 

 americanus (Walbaum), an important species in 

 local New England commercial and sport fishing 

 industries, occurs from Chesapeake Bay to the 

 northern shore of the Gulf of St. Lawrence 

 (Bigelow and Schroeder 1953). The adults dis- 

 perse into cooler offshore waters as temperatures 

 rise, but move back into embayments and es- 

 tuaries in the fall. Spawning occurs in shoal wa- 

 ters of these areas from February to mid-May with 

 the maximum in Rhode Island waters occurring 

 in March (Perlmutter 1947; Bigelow and 

 Schroeder 1953; Pearcy 1962). Winter flounder 

 spawn demersal eggs, which range from 0.74 to 

 0.85 mm in diameter when fertilized. Hatching 

 occurs in 15 to 18 days at 3° to 4°C, the tempera- 

 ture normally encountered in the natural envi- 

 ronment (Bigelow and Schroeder 1953). 



This paper reports the optimum temperature 

 and salinity ranges for the development and sur- 

 vival of winter flounder embryos and larvae and 

 discusses the relationship between the two fac- 

 tors as it affects embryo development. An earlier 

 study (Scott 1929) indicated some of the effects of 

 temperature and salinity as separate factors on 

 the hatching of winter flounder eggs but pre- 

 sented no data on possible interaction of the two. 

 Forrester and Alderdice (1966) and Alderdice and 

 Forrester (1968, 1971a, b) working on the effects 

 of temperature and salinity on the embryonic de- 

 velopment of the English sole, Parophrys uetulus; 

 petrale sole, Eopsetta jordani; and Paciflc cod, 

 Gadus macrocephalus , respectively, indicated a 



'Northeast Fisheries Center Narragansett Laboratory, 

 National Marine Fisheries Service, NOAA, Narragansett, 

 RI 02882. 



relationship between the two factors, which 

 influenced early development, hatching time, and 

 viable hatch. 



METHODS AND MATERIALS 



Ripening adult winter flounder were captured 

 by trawl on 29 October 1970 at a depth of 23 to 30 

 m in Block Island Sound. Surface waters were 

 15°C, and a bottom temperature of 12°C was es- 

 timated for that area (Colton and Stoddard 1973). 

 The live fish were transported to the laboratory 

 where they were held in running water aquaria 

 until they were ripe in early February when am- 

 bient water temperature was 3°C. The fish were 

 fed clam worms, earthworms, and cut up clam 

 during the holding period. Eggs were stripped 

 into polyethylene dishpans, fertilized, and coated 

 with diatomaceous earth to prevent clumping, ac- 

 cording to the technique of Smigielski and Arnold 

 (1972). Fertilized eggs were transferred to incu- 

 bation baskets and held at 3°C in running seawa- 

 ter (32% salinity) for 24 h when normal develop- 

 ment could be distinguished. Day 1 embryos were 

 in the early blastoderm stage when the experi- 

 ments were started. Three separate experiments 

 were run at salinities ranging from 0.5 to 45%, 

 and at temperatures of 3° to 14°C. Each experi- 

 ment was run in duplicate. 



To avoid bias, all salinities were prepared by 

 adding Instant Ocean ^ salts to normal seawater 

 (32%) to bring the salinity up to 50%. Experimen- 

 tal salinities were then made by diluting the 

 stock salinity with distilled water. Each salinity 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



Manuscript accepted March 1975. 



FISHERY BULLETIN: VOL. 74, NO. 1, 1976. 



52 



