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X10 of pls. in- by ted me ire oa ire to ire ng. ing ~u- 50 re- nd to ~ °/ ° :o- ~e- by Bch ate al, per ng nd N- rs; ies 'd. ed he Ily )). ~r- Results Experiment 1 Median time to 50% mortality of unfed razorback sucker larvae was between 24 and 25 d post-hatch- ing. The majority of larvae died between 20 and 30dpnst-hatching. Average TL at death was 9.6 ± 0.2 mm (n = 28). Experiment 2 No mortality was experienced by larvae receiving food on day seven post-hatch. Larvae that began receiving food beginning on d 11, 15, and 19 post- hatch had respective mortalities of 10.0, 10.0, and 26.7%. There were no significant differences among 7, 11, 15, and 19d (Table 1}. Highest death rates occurred when larvae were deprived of food for 27 (86.7%) and 31 d (93.3%), with no statistical Table 1. Experiment 2. Comparison of percentage mortalities (top) and total length (TL: bottom) ± the standard ercor (SE) after 50 d of life for treatments in which food was withheld from razorback sucker larvae (or 7, 11, 15, 19, 23, 27, and 31 d after hatching. Differing letters in parentheses denote significant dif- ferences (p<0.05) in pairwise comparisons of treatment means. Age at initial feeding Mean mortality, % ± SE (d after hatching) 7 0.0 (x) 11 lo.o ± s.s (x) 15 10.0 ± 10.8 (x) 19 26.7 ± 13.3 (xy) 23 56.7 ± 16.7 (yz) 27 86.7 ± 6.6 (z) 31 93.3 ± 3.3 (z) Number Mean TL Range specimens mm ± SE TL (mm) 7 24 23.2 ± 0.5 16.1-25.9 11 27 22.4 ± 0.4 18.7-27.7 15 28 21.7 ± 0.4 17.6-24.7 19 20 19.7 ± 0.4 15.4-23.5 23 1] 18.8 ± 0.6 15.8-21.9 27 4 17.3 ± 0.6 15.5-18.0 31 2 iS.R 15.1-16.4 7s differences between the last values. As in Experi- ment 1, the majority died between 20 and 30 d at an average size of 9.3 ± 0.1 mm TL (n = 35). Surviv- ing larvae were larger (n = 24, 23.0 ± 0.5 mm) when fed from d 7 and smaller (n = 2, 15.1 and 16.4 mm) when first fed at d 31 (Table 1). Experiment 3 Mortality was greatest and not significantly differ- ent when larvae were fed either 5 or 10 nauplii 1-' (86.7 ± 3.3 and 73.3 ± 3.3%). Larvae fed 50, 100, 500, and 1000 nauplii 1-' all had < 20% mortality, with no significant differences among treatments (Table 2). Death rates leveled when larval mortal- ity was sufficient to provide survivors at least 10 to 20 nauplii fish-' feeding-' in the 5- and 10-nauplii 1-' treatments (Table 3). Most larval deaths were again between 20 and 30 d, at a mean of 10.1 ± 0.2 mm TL (n = 25). Larvae surviving 50 d (Table 4) on rations of 5 and 10 nauplii (-' did not differ significantly in TL. Those larvae receiving 100 nau- plii 1-' were significantly larger than those in the 10 nauplii 1-' treatment, but significantly smaller than larvae receiving 500 and 1000 nauplii 1-'. Threshold density of prey, beyond which mortal ities did not decrease significantly, was 50 nauplii 1-' (Table 2). The minimum densities yielding < 50% mortality were between 10 and 50 nauplii 1-'. At 50 nauplii 1-', each larva was exposed to -~- 20 nauplii 3 times d-'. In treatments receiving 5 and 10 nauplii 1-', mortality during the experiment Table 2. Experiment 3. Percentage mortality of razorback suck- er Larvae fed 5,10, 50,100, 500, and 1000 brine shrimp nauplii I-' three times d-' ± standard ercor (SE). Differing letters in pa- rentheses denote significant differences (p<0.05) in pairwise comparisons of treatment means. Nauplii I-' Mean mortality, % ± SE 5 86.7 ± 3.3 (x) 10 73.3 ± 3.3 (x) 50 18.3 ± 6.6 (y) 100 20.0 ± 5.8 (y) 500 6.7 ± 3.8 (y) 1000 10.0 ± 5.8 (y) %4 ~k ~~ ;: .; ~` a ;;: `, ~ `_i t • 1 ';