Powell and Henley: Larval development of Paralichthys albigutta and P. lethostigma 



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Methods 



Adult P. albigutta and P. lethostigma were collected 

 in the early fall during 1991 and 1992 from commer- 

 cial pound nets in Core Sound, North Carolina. Indi- 

 vidual fish were tagged and meristic data (gill-raker 

 and anal-ray counts) were used to confirm identifi- 

 cation (Gutherz, 1967). Spawning was induced with 

 the aid of hormones as described by Smigielski ( 1975). 

 For P. albigutta three different females were fertil- 

 ized by a single male. Females were injected with 

 carp pituitary hormone (2 mg/kg fish) two or three 

 times to promote hydration. Eggs were fertilized on 

 14 and 19 February 1992. For P. lethostigma, a total 

 of four different males and four different females 

 were spawned. Eggs were fertilized on 17 December 

 1992, 24 February, and 2 March 1993. 



Eggs and sperm from both species were manually 

 stripped into 1-L bowls; eggs were fertilized, and 

 embryos incubated in 100-L black-sided tanks. 

 Paralichthys albigutta larvae were reared in uncir- 

 culated, filtered water at a mean temperature of 19°C 

 (range: 14-24°C) and a mean salinity of 30 ppt (range: 

 28-30 ppt). Paralichthys lethostigma larvae were 

 reared at a mean temperature of 18°C (range: 16- 

 19°C) and a mean salinity of 32 ppt (range: 23-42 

 ppt). Rotifers and Artemia nauplii were provided to 

 young (<15 days old) and older (>15 days old) larvae, 

 respectively Only three P. lethostigma larvae were 

 alive after approximately 35 days, limiting the 

 amount of material available for this species. Eggs 

 and larvae were preserved in 10% buffered forma- 

 lin. Counts of meristic characters were obtained from 

 cleared and stained specimens (Potthoff, 1984). All 

 measurements and observations were made with a 

 Wild M5A stereomicroscope equipped with an ocu- 

 lar micrometer. 



The larval period was separated into preflexion, 

 flexion, and postflexion stages — the three stages as- 

 sociated with the development of the caudal fin be- 

 fore, during, and after the upward flexion of the no- 

 tochord tip. During preflexion and flexion, larval body 

 length was measured from the tip of the snout to the 

 tip of the notochord (notochord length, NL). In 

 postflexion larvae (defined when 6 upper + 7 lower 

 principal rays were formed) body length was mea- 

 sured from the tip of the snout to the base of the 

 hypural plate (standard length, SL). 



Postflexion larvae and transforming juveniles of 

 P. albigutta and P. lethostigma captured in Onslow 

 Bay off North Carolina during the winter of 1990 

 and 1991 were used for 1) comparison with labora- 

 tory-reared specimens and 2) illustrations and in- 

 vestigation of pterygiophore patterns. This material 

 also was used to determine the size when meristic 



characters develop for P lethostigma because material 

 from laboratory-reared specimens was limited for this 

 species. Observations on pterygiophore patterns and 

 meristic characters were made on cleared and stained 

 specimens. Larval material is deposited at the Beau- 

 fort Laboratory under the care of the senior author. 



Results 



Eggs and recently hatched larvae 



Paralichthys albigutta Eggs were spherical and 

 had a mean diameter of 0.87 mm (range: 0.84-0.90 

 mm, n=44). One oil globule was present and had a 

 mean diameter of 0.18 mm (range: 0.17-0.19 mm, 

 n=44). The yolk was homogenous, the chorion 

 smooth, and the perivitelline space (in live eggs) nar- 

 row (ca. 0.2 mm). Pigment was first observed in the 

 caudal area of embryos just after blastopore closure 

 (Fig. 1A). On embryos from late-stage eggs (from tail 

 twisting to hatching), pigment occurred on the oil 

 globule, sparsely in the head region, and was most 



B 



Figure 1 



Laboratory-reared eggs and newly hatched larvae of gulf 

 flounder, Paralichthys albigutta: (A) middle stage: left, 

 anterior view; right, posterior view; (B) late stage: left, 

 anterior view; right, posterior view; and (C) 2.2-mm-NL 

 newly hatched yolk-sac larva. 



