WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2016 35 TABLE 2. Particle size, sinking rates (cm/sec), and age offered (dph) for the experimental diets used in microdiet feed trials for white seabass and California yellowtail. Diet Type Sinking Rate Age Offered (size) (cm/sec) (dph) AVG±SD OTO (250-360 µm) 0.53 ± 0.13 15 to 20 OTO (360-650 µm) 0.93 ± 0.15 18 to 35 OTO (580-840 µm) 1.21 ± 0.18 25 to 40 GEMMA (100-200 µm) 0.29 ± 0.07 15 to 20 GEMMA (200-400 µm) 0.64 ± 0.17 18 to 35 GEMMA (300-500 µm) 1.18 ± 0.15 25 to 40 PARA (250-425 µm) 0.59 ± 0.18 15 to 20 PARA (425-710 µm) 1.34 ± 0.26 18 to 40 MEM (500-800 µm) 1.44 ± 0.24 15 to 40 TABLE 3. Proximate composition of two experimental larval microdiets (MEM and PARA) and two commercial diets (OTO and GEMMA). Values with lower case superscripts within columns are significantly different (P<0.05). Diet Type Moisture Fat Protein (% ± SD) (% ± SD) (% ± SD) MEM 5.9 ± 0.01a 25.6 ± 0.2a 51.9 ± 0.1a PARA 5.2 ± 0.2b 26.7b 51.1 ± 0.3a OTO 6.4 ± 0.1a 15.6 ± 0.3c 53.9 ± 0.1b GEMMA* 6.5 ± 0.1 17.4 ± 0.2 56.7 ± 0.1 *GEMMA data from Bonaldo et al. 2011 TABLE 4. Length, weight, and survival of 40 dph white seabass (WSB) and California yellowtail (CYT) fed two different weaning diets. For each species, values with lower case superscripts within columns are significantly different (P<0.05). Species Treatment Weight Standard Length Survival (g ± SD) (mm ± SD) (% ± SD) WSB PARA 0.11 ± 0.03 16.9 ± 1.8 7.2 ± 1.1 MEM 0.11 ± 0.04 17.2 ± 1.9 5.2 ± 0.9 OTO 0.13 ± 0.04 18.3 ± 2.6 6.2 ± 1.8 CYT PARA 0.11 ± 0.13 14.7 ± 2.7 8.1 ± 4.2 GEMMA 0.14 ± 0.07 17.7 ± 3.1 5.1 ± 0.5 OTO 0.11 ± 0.07 16.4 ± 2.9 3.3 ± 2.4 There were no differences in growth or survival of white seabass fed MEM, PARA, or OTO (Table 4). There were no differences in growth or survival of California yellowtail fed PARA, OTO, and GEMMA (Table 3). However, there was a trend of greater survival (although not significant) of fish of both species fed the PARA diet (white seabass: 7.2 ± 1.1 percent; California yellowtail: 8.1 ± 4.2 percent) compared to that of fish fed the commercial diets (white seabass: OTO 6.2 ± 1.8 percent; California yellowtail: OTO 3.3 ± 2.4 percent, GEMMA 5.1 ± 0.5 percent). Based on larval performance, the PARA diet had the appropriate physical characteristics for white seabass and California yellowtail larvae. Feeding Incidence Gut contents were examined every three days from 20 to 40 dph. Gut content analyses was accomplished by sub-sampling ten larvae from each tank one hour after the first feeding of the day at 0800 h. Microparticuate diets were the only feeds offered to larvae on sample days. Larvae were placed on a microscope slide and gut contents dissected so that food items could be identified. Feeding incidence was calculated by dividing the number of larvae observed with food in the gut by the total number of larvae sampled (N = 10). Enriched second-instar Artemia (1-3/mL) were offered to larvae from 15 to 35 dph. Larvae were transitioned from Artemia to microdiets starting at 16 dph by co-feeding with microdiet. Live prey was added four times daily at 0700, 1000, 1300, and 1600 h. Microdiets were fed manually four times daily and with an automatic feeder2 that provided feed for 18 h. Beginning at 16 dph, 5 g of each microdiet was offered to each experimental tank. This amount was increased to 10 g at 27 dph and increased again at 35 dph to 15 g. Growth and Survival Growth was measured on subsamples of 20 larvae per replicate at 16, 23, 30, and 40 dph. Larvae were euthanized with MS-222 prior to making measurements. Twenty larvae were placed under a MZ16 Macro5 microscope (Fig. 4), a digital photograph taken, and standard length (SL) measured to the nearest 0.1 mm using Image-Pro Plus6 software. Each larva was weighed to the nearest 1 g. Survival was determined at 40 dph by individually counting the number of the fish remaining in each experimental tank. (CONTINUED ON PAGE 36)
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