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Fishery Bulletin 92|2). 1994 



location of head spines followed Gregory (1933). One 

 larva was cleared with trypsin then stained with 

 alizarin in each millimeter (mm) length interval to 

 examine small serrate ridges around the orbit (i.e. 

 circumorbital bones), and spines and ridges on the 

 head. We examined spines on the occipital and fron- 

 tal bones with a scanning electron microscope 

 (SEM), and specialized spinous scales with a com- 

 pound microscope. Fin rays were counted when first 

 segmented and spines when present. Representative 

 specimens were illustrated with the aid of a cam- 

 era lucida. 



Estimates of larval density (number of larvae/ 

 100m 3 of water) and catch (number of larvae/10 tow) 

 were calculated by month. Months were combined 

 across years because not all months were sampled 

 every year (Appendix Table). Densities for stations 

 where larvae were collected (i.e. positive catch sta- 

 tions) were calculated by dividing sum of larvae 

 collected in bongo net tows by total positive catch 

 station volume of water filtered (VWF) and multi- 

 plying the result by 100. In addition, an overall (i.e. 

 grand) density estimate was calculated by dividing 

 sum of larvae by total VWF for all stations sampled 

 that month and multiplying the result by 100. Over- 

 all density more closely reflects the density of lar- 

 vae throughout the area by including the total vol- 

 ume of water filtered in calculations. Estimates of 

 larval catch in neuston nets were calculated by di- 

 viding sum of larvae by number of positive catch 

 neuston stations or by total number of neuston sta- 

 tions sampled and multiplying the result by 10. 

 Estimates of larval density and catch included sta- 

 tions at long. >88°00' W because only one Atlantic 

 spadefish larva was collected east of Mobile Bay, 

 Alabama. Similarly, estimates were calculated only 

 for June through August because May and Septem- 

 ber had but one positive catch station each. 



Temperature and salinity data were gathered 

 from the sea surface. Positive catch station hydro- 

 graphic data were multiplied by total number of 

 larvae collected at each station to obtain a monthly 

 median and mean. Hydrographic data were also 

 combined across months to obtain an overall (i.e. 

 grand) median and mean. This method gives weight 

 to distribution of larvae rather than to distribution 

 of stations. We used a percent cumulative frequency 

 of >85%> for defining the relation between distribu- 

 tion of Atlantic spadefish larvae and water tempera- 

 ture, salinity, and station depth. Percent frequency 

 indicates the range of hydrographic conditions most 

 often associated with occurrences of larvae. Proc 

 Univariate was used to calculate median, mean, and 

 percent cumulative frequency statistics (SAS Insti- 

 tute, 1985). 



Results 



Morphometries and pigmentation 



Early larvae were rotund and deep-bodied; body 

 depth was >50% SL by 3.5 mm and >60% by 9 mm 

 (Table 1). Atlantic spadefish became increasingly 

 deep-bodied and laterally compressed after noto- 

 chord flexion. There were 24 myomeres but these 

 became obscured by pigment in postflexion larvae. 

 The head was large and averaged about 35% SL in 

 larvae >3.0 mm. Head profile became steep and in- 

 creasingly deeper than long. The mouth was termi- 

 nal and the upper jaw reached to about mid-eye. 

 Eyes were round and large, ranging from 36 to 43% 

 of head length in larvae >3.5 mm (i.e. about 14-15% 

 SL). The gut was tightly coiled in a single loop and 

 the anus was slightly beyond mid-body (usually 

 55-60% SL). 



Pigment was largely restricted to the anterior-half 

 of the body in early preflexion larvae of Atlantic 

 spadefish. On the head of a 1.8-mm larva, external 

 pigment was scattered over the mid- and hindbrain, 

 nape, opercle, branchiostegal membrane, and along 

 the isthmus and quadrate. Internally, pigment was 

 present along and above the anterior portion of the 

 notochord, and a single median patch was observed 

 on the roof of the mouth. On the abdomen, there was 

 a patch of pigment on the visceral mass immediately 

 anterior to and below the pectoral-fin base. In ad- 

 dition, melanophores were scattered over the pecto- 

 ral fin base and its finfold and were distributed lat- 

 erally over the visceral mass and hindgut. A row of 

 about 20-25 small, closely spaced melanophores 

 were visible along the ventral midline of the tail in 

 early larvae. Number of melanophores along the 

 ventral midline of the tail decreased as larvae grew. 

 Melanophores on the nape, opercle, pectoral-fin 

 base, and visceral mass formed a "swath" of pigment 

 over the anterior 55-60% of the body by 2.5-3.0 mm 

 (Fig. 1). By 3.0—3.5 mm, internal melanophores were 

 visible anteriorly on the forebrain and laterally on 

 the midbrain above the eye. Melanophores were also 

 scattered both internally and externally over the 

 hindbrain both anterior to and posterior to the base 

 of the supraoccipital crest. By early postflexion (i.e. 

 5.0 mm), the head and abdomen were densely pig- 

 mented but the posterior portion of the body was 

 sparsely pigmented. Pigmentation increased on the 

 posterior-half of the body as larvae grew, and by 10.0 

 mm the entire body was pigmented (Fig. 1). Consoli- 

 dation of pigment into bands began on the head of 

 Atlantic spadefish larvae with one band visible 

 above the eye by 10.0-11.0 mm. This band of pig- 

 ment was enclosed by indefinite, pale crossbars. The 



