192 



Fishery Bulletin 93(1), 1995 



each treatment: from OTC and alizarin treatments 

 for otolith mark examination, from wire treatments 

 for wire removal, and from other treatments for fu- 

 ture otolith analysis. All samples were preserved by 

 freezing. In estimating percent survival, it was as- 

 sumed that all fish that were sacrificed (alive and 

 healthy at time of sample) would have survived the 

 68-d experimental period. The actual survival of sac- 

 rificed fish would be lower than 100%, but the differ- 

 ence in survival rate among treatments would be 

 expected to increase if actual survival rates for all 

 fish were known. 



Whole sagittal otoliths were removed from OTC and 

 alizarin treatments and viewed with an Olympus BH- 

 2 compound microscope under 100-W ultraviolet light. 

 When fluorescent marks were not visible on whole 

 otoliths, they were sectioned and polished for in- 

 creased resolution (Secor et al., 1991b; Szedlmayer 

 and Able, 1992). Wire tags were located by mak- 

 ing a sagittal incision of the epaxial muscle and 

 examined under a Nikon stereo-microscope. If 

 wire tags were not located by dissection, fish were 

 X-rayed to locate tags. 



We compared instantaneous mortality rates 

 with analysis of covariance (ANCOVA) and per- 

 cent tag retention with a randomized block 

 analysis of variance (ANOVA) with day as 

 blocks and marking method as the factor (Zar, 

 1984). We compared standard lengths (SL) and 

 weights over marking method with ANOVA for 

 each sample date. If significant differences 

 (P<0.05) were detected, we compared the means 

 (ANOVA) or slopes (mortality; ANCOVA) with 

 Newman-Keuls range test (Zar, 1984). 



Results 



Instantaneous mortality rates (log per- 

 cent survival=-Zrf + Y) for OTC 

 (-Z=0.0013, r 2 =0.92), alizarin 

 (-Z=0.0014, r 2 =0.80), and wire 

 (-Z=0.0016, ^=0.78) marking were sig- 

 nificantly less than those for plastic 

 (-Z=0.0023, ^=0.90), red (-Z=0.0025, 

 r 2 =0.96), and green treatments 

 (-Z=0.0033, r^O.92; Fig.l). Survival 

 curves showed similar patterns with 

 higher mortality in the first 40 days; 

 thereafter mortality was reduced 

 (Fig. 1). 



Percent mark retention of alizarin, 

 OTC, and wire tags were signifi- 

 cantly greater than those of other 

 treatments. The highest mark reten- 



tion was observed for OTC- and alizarin-marked fish 

 (100%; Table 1). Wire-marked fish also showed high 

 retention rates (85-100 %). Red-, green-, and plas- 

 tic-marked fish showed significant declines in tag re- 

 tention over the 68 days (Table 1). 



Mean SL and weight showed no significant differ- 

 ence among treatments on day 1, 25, 48, and 68 (Tables 2 

 and 3). Growth rates were similar among all treatments: 

 1.0-1.1 mm SlVd and 0.5-0.6 g wet wt/d (Tables 2 and 3). 



Discussion 



Wire tags provided the best overall performance of 

 the marking methods tested over this two-month 



Table 1 



Percent mark retention among sample days of age-0 red drum, Sciaenops 

 ocellatus, marked by one of six methods: wire = coded wire microtag; plastic = 

 external plastic tag; red = red fluorescent paint; green = green fluorescent 

 paint; OTC = oxytetracycline dihydrate; and Ali = alizarin complexone. Num- 

 bers in parenthesis are sample sizes. Treatments with different letters are 

 significantly different (P<0.05). 



Marking method 



Day 



OTC 



Ali" 



Wire" 



Red 6 



Plastic* Green 6 



25° 



48 a6 



68 c 



100.0(21) 100.0(20) 90.0(20) 80.5(82) 78.2(78) 42.3(78) 

 100.0(20) 100.0(20) 100.0(20) 55.8(52) 49.1(53) 39.1(46) 

 100.0(19) 100.0(21) 85.0(20) 14.8(27) 24.1(29) 16.0(25) 



