34 MARCH 2016 • WORLD AQUACULTURE • WWW.WAS.ORG characteristics that may elicit a feeding response from larval fish, directly impacting ingestion and, secondarily, digestion. The ability to wean larvae to formulated diets early in development is based on physical characteristics of the diet and on the development of sensory and digestive organs in larvae (Hamre et al. 2013). Prey accessibility is defined by its size, shape, and ability to escape from predators, with size being the primary characteristic for marine finfish larvae. Mouth gape and esophageal diameter are limiting factors (Russo et al. 2009) and the range of accessible particle sizes increases as the larvae grows. The PARA and OTO diets had similar size ranges; PARA: 250-425 µm and 425-710 µm, OTO: 250-360 µm, 360-650 µm, and 650-850 µm. The GEMMA diet also had three size ranges: 100-200 µm, 300-400 µm, and 300-500 µm. The MEM diet had only one size range, 500-800 µm. Smaller-size diets (PARA, OTO, and GEMMA) were fed from 15 to 20 dph; medium-size diets were fed from 18 to 35 dph, and large-size diets were fed from 25 to 40 dph. The MEM diet was only one size and was fed for the trial duration (Table 2). Live prey swim in the water column and movement captures the attention of fish larvae. Therefore, microdiets need to sink fast enough to draw attention but slow enough to allow consumption (Langdon and Barrows 2011). The sinking rate of each diet was measured by placing 1 g of diet in a 1-m deep clear cylinder and TABLE 1. Ingredient composition of experimental microdiets (PARA and MEM marked with yttrium oxide). Ingredient Composition g/kg Squid Meala 392 Krill Mealb 256 Anchovy Oilc 105 Lecithind 100 Wheat Gluten Meale 90 Vitamin Premix 702f 20 Dicalcium Phosphateg 20 Taurineh 15 Astazanthini 5 Stay-Cj 2 a Scoular, Dosidigus gigas, Peru, 705 g/kg crude protein b Antarctic Sea Fisheries, F/V Betanzos, 638 g/kg crude protein c Menhaden oil, Virginia Prime, Omega Protein Corp., Houston, Texas d American Lecithin Company, Soy lecithin, Oxford, Connecticut e Manildra Group USA, Shawnee Mission, Kansas, 778 g/kg protein f ARS 702 DSM Nutritional Products, Basel, Switzerland. Provides per kg diet before processing; vitamin A 19300 IU; vitamin D 13200 IU; vitamin E 264 IU; vitamin K3 2.2 gm: thiamin mononitrate 18.2 mg; riboflavin 19.2 mg; pyridoxine hydrochloride 27.4 mg; pantothenate DL-calcium 93; cyancobalamin 0.06 mg; nicotinic acid 43.6 mg; biotin 0.68 mg; folic acid 5.0; inostitol 1200. g Wilbur-Ellis, Ogden, Utah h NB Group Co. LTD., Shangdong, China i Carophyl Pink 10, DSM Nutritional Products, Basel, Switzerland j Ascorbic acid Stay-C 35, DSM Nutritional Products, Basel, Switzerland timing the descent of particles. The OTO and PARA diets had a similar size and sinking rate (Table 2). GEMMA diets > 500 µm were not offered but sinking rates for the larger GEMMA size class were similar to both larger sizes of OTO and PARA. MEM diets only had one size class (500-800 µm) and sinking rates were faster for the MEM particle (1.44 ± 0.24 cm/sec) as compared to the smallest available OTO (0.53 ± 0.13 cm/sec) and PARA (0.59 ± 0.18 cm/sec) particles. However, the sinking rate of MEM particles was similar to that of the largest OTO and PARA particles. Experimental Setup Fish larvae (15 dph) were stocked at 5/L (1,500 larvae/ tank) into an experimental system consisting of 24 black, conical-bottom, 320-L tanks (Fig. 3). Tanks were supplied with temperature-controlled (21 C for California yellowtail, 18 C for white seabass) recirculating seawater at 2-3 L/min. A 500-µm mesh containment screen was placed in the center of each tank with an aeration ring to maintain good water circulation. Fluorescent lights were placed 70 cm above tanks for illumination (800-1,500 lux lights1) and were set at a continuous photoperiod until 30 dph and then were placed on a 18-h light and 6-h dark photoperiod. There were three treatments and four replicate tanks in each trial. The duration of each trial was 25 days (15 to 40 dph). FIGURE 3. Conical tanks (320 L) to evaluate microdiets for larval white seabass and California yellowtail. FIGURE 4. Preparing fish larvae for measurement of length and weight.
RkJQdWJsaXNoZXIy MjExNDY=