186 



Fishery Bulletin 90(1). 1992 



Growth comparisons 



Marginal growth increments seemed to form from 

 evening through early morning (Table 4). The allo- 

 metric relationship (logio radius = 0.126 logioSL + 

 1.413; r^ 0.91) between otolith radius and standard 

 length of 131 larvae also suggested a daily periodicity 

 in otolith increment formation (Hales 1987). 



Estimates of the length at hatching (L(0)) for gulf 

 menhaden provided by the Laird- 

 Gompertz model 3.4mm SL (Fig. 

 1; Table 5), closely approximate 

 the length-at-hatching of larvae 

 incubated in the laboratory at a 

 temperature of 20°C, 2.6-3.0mm 

 SL (Hettler 1984). Estimates of 

 L(0) for round herring, about 1.2 

 mm SL, however, are consider- 

 ably lower than the lengths re- 

 ported for larvae hatched in the 

 laboratory: 3. 8-4. 0mm body 

 length from eggs collected in the 

 South Atlantic and incubated at 

 20.5°C (O'Toole and King 1974) 

 and 6.0 mm SL from eggs col- 

 lected in the Pacific and incu- 

 bated at 24-26°C (Miller et al. 

 1979). If the interval from hatch- 

 ing to deposition of the first 

 growth increment is shorter in 

 reality than the assumed 5 days, 

 the Laird Gompertz growth 

 curve would shift to the left, 

 yielding a greater value for L,o), 

 but the form of the growth curve, 

 i.e., the growth rate, would re- 

 main the same. 



Round herring grew faster 

 than gulf menhaden through the 

 first 20-40 days; gulf menhaden 

 exhibited faster growth than 

 round herring thereafter (Fig. 2). 

 The fastest growth rate (=0.85 

 mm/day) for round herring lar- 

 vae occurred at about 15 days. 

 Average growth rates through 

 27 days for December 1980 were 

 0.71 and 0.46 mm/day for round 

 herring and gulf menhaden; 

 average rates through 50 days in 

 •February 1981 were 0.45 and 

 0.34 mm/day. Annual differences 

 in larval gulf menhaden growth 

 are discussed in Warlen (1988). 



Table 4 



Percentage of round herring larvae with partially formed (nar- 

 row) or completed (wide) marginal otolith growth increments 

 collected at three different times of day. 



Time of capture 

 (h) 



No. of 

 fish 



Percentage 



Partially formed Completed 



1800 

 2400 

 0600 



9 



10 

 6 



22 



40 

 100 



78 



60 

 



Etrumeus teres 



12 14 16 18 20 22 24 26 



20 25 30 35 



20 25 30 35 40 



ESTIMATED AGE (DAYS) 



Figure 1 



Growth of larval round herring Etrumeus teres and gulf menhaden Brevoortia patronus 

 collected in December 1980 (A) and February 1981 (B) in the northern Gulf of Mexico. 

 The log form of the Laird-Gompertz model was used to describe the growth of both species 

 (numbers indicate location of coincident data points). 



