NOTE Rom^n-Rodriguez and Hamm ann: Age and growth of Totoaba macdonaldi 
625 
Table 2 
Observed and predicted mean standard length at year-class midpoints, n = sample size. SD = standard deviation. VBGM = von 
Bertalanffy growth model. BC = back-calculated model. 
Year class 
midpoint (yr) 
n 
Observed SL: 
mean (mm) 
Observed SD 
Predicted 
VBGM (mm) 
Predicted VBGM 
BC (mm) 
0.5 
66 
218 
66 
216 
319' 
1.5 
10 
503 
75 
525 
595 
2.5 
1 
740 
— 
750 
797 
3.5 
1 
1,080 
— 
914 
945 
4.5 
0 
— 
— 
1,034 
1,053 
5.5 
0 
— 
— 
1,121 
1,133 
6.5 
0 
— 
— 
1,184 
1,192 
7.5 
1 
1,260 
— 
1,231 
1,234 
8.5 
0 
— 
— 
1,264 
1,266 
9.5 
0 
— 
— 
1,289 
1,289 
10.5 
1 
1,271 
— 
1,307 
1,306 
11.5 
0 
— 
— 
1,320 
1,318 
12.5 
2 
1,363 
38 
1,329 
1,327 
13.5 
5 
1,318 
88 
1,336 
1,334 
14.5 
4 
1,309 
102 
1,341 
1,339 
15.5 
5 
1,340 
24 
1,345 
1,342 
16.5 
1 
1,390 
— 
1,348 
1,345 
17.5 
1 
1,300 
— 
1,350 
1,347 
18.5 
0 
— 
— 
1,351 
1,348 
19.5 
1 
1,280 
— 
1,352 
1,349 
20.5 
0 
— 
— 
1,353 
1,350 
21.5 
1 
1,490 
— 
1,354 
1,350 
22.5 
0 
— 
— 
1,354 
1,351 
23.5 
0 
— 
— 
1,354 
1,351 
24.5 
1 
1,453 
— 
1,354 
1,351 
Total 
101 
1 Otolith core to margin measurements along ventral arm of sulcal groove were used for year-class 0, and predicted lengths were derived from the 
resulting equation. 
Flanagan, 1973; Molina et al. 1 ), versus otoliths, as 
used in our study (Table 3), the greatest difference is 
found with Nakashima (1916). He estimated the 
maximum age for a fish of 1,980 mm (SL) to be nine 
years; our study shows that this fish could be older 
than 24 years. The von Bertalanffy parameters we 
estimated are very similar to those reported by 
Berdegue (1955) and Flanagan ( 1973). In the Molina 
et al. 1 study there was a large underestimation of 
maximum age in comparison with our results, re- 
flected in the K value. This difference could be due 
to our use of a greater range of year classes from 
young-of-the-year to adults, whereas Molina et al. 1 
used only adult fish. Juveniles or young-of-the-year 
should be included to fit the von Bertalanffy growth 
curve because if only adults are used, there is a ten- 
dency to obtain low K values (Beckman et al., 1990). 
Scales often result in the underestimation of age 
(Beamish and McFarlane, 1987) owing to difficulty 
in reading, especially in the outer rings which are 
very close. Furthermore, there is a possibility of us- 
ing regenerated scales in which the first rings that 
were formed are not included. Authors working with 
sciaenids have mentioned that reading scales is easier 
for short-lived species, like some species of Cy noscion 
(Villamar, 1972; De Vries and Chittenden, 1982). 
On the basis of growth and otolith marks observed 
in two juveniles held in captivity, we suggest that 
ring formation in totoaba from the Gulf of California 
is annual; annual deposition patterns have been re- 
