WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2017 37 Study Methods Larvae were obtained from eggs spawned naturally in spawning tanks and rearing was carried out in indoor 4-m³ capacity fiberglass tanks at AMSC hatchery. Newly hatched larvae (2.1 mm) were stocked in eight rectangular, 4-m³, indoor fiberglass larval rearing tanks (LRTs) at an initial density of 15 ± 2/L. Rearing trials were performed until larvae were 40 days post hatch (dph) with the following two feeding regimes: 1) only rotifers during first feeding (R regime) and 2) copepod co-fed with rotifers during first feeding (RC regime). Each feeding regime was replicated in four tanks. No major differences in water quality was observed among tanks during the rearing period. Water temperature was 24.5 ± 1.3 C, dissolved oxygen was 5.2 ± 0.8 mg/L, ammonia was 0.16 ± 0.04 mg/L, nitrite was 0.019 ± 0.002 and pH was 7.8 ± 0.4. Green algae (Nannochloropsis sp.) was added to all LRTs from 1 to 25 dph at a daily rate of 50 to 100 L/tank to maintain 1-3 × 104 cells/mL. The feeding protocols for rotifers, Artemia, artificial feeds and water exchange rates were as described by Yousif et al. (2016). Copepods were collected daily from shrimp ponds with a large plankton net and a submersible pump at night and fractions were separated through 100-µm and 150-µm mesh which were dominated by nauplii and copepodites respectively. The copepods were a mix of calanoid, cyclopoid and harpactocoid types. Adult copepods were fed to later-stage larvae (> 8 dph). Larval length was measured every five days by collecting ten larvae from each tank and calculating the average. At the end of the rearing period (40 dph), all larvae were harvested and graded and the survival calculated. Twenty-five individuals from each tank were collected for weight measurement and estimation of the size distribution of the population. All experimental data are presented as means ± SD of four replicates. Mean body length, mean body weight and survival of the two treatments were compared using ANOVA. All means were compared using Tukey’s test. Increasing market demand and declining natural supplies of orangespotted grouper Epinephelus coioides has made this species the top potential candidate for aquaculture in the United Arab Emirates (UAE). However, reliable and consistent fingerling production remains a major bottleneck for expansion of commercial grouper aquaculture (Ma et al. 2013, Yousif et al. 2016). High mortality rates have occurred when larvae switch from endogenous to exogenous feeding (Toledo et al. 1999), attributed to the small mouth size at the first feeding stage and limited yolk reserves at the time of hatching (Kohno et al. 1997). Successful larval rearing depends on the availability of appropriately sized and nutritionally adequate food for larvae. In nature, copepod nauplii are the major food for marine fish larvae during first feeding stages (McKinnon et al. 2003). Different life stages of copepods are important prey for different life stages of fish; many marine fish larvae continue to feed on larger copepods until they reach metamorphosis. Copepod nauplii and copepodites offer a diverse size spectra and nutritious prey that can meet the specialized needs of small fast-growing fish larvae (Stoettrup 2000). Orange-spotted grouper larvae fed copepod nauplii have better survival and growth thereafter compared to those fed rotifers only (Doi et al. 1996). Grouper larvae seem to catch copepod nauplii easier than rotifers. Other reports indicate that the levels of n-3 highly unsaturated fatty acids — necessary for development of marine larval fish — in rotifers are lower than those in copepods (Sergent 1999, Toledo et al. 1999, Ma et al. 2013). A larval rearing trial was conducted at the Aquaculture and Marine Studies Center (AMSC), Abu Al Abyad, Abu Dhabi, to evaluate the potential of improving grouper larvae production by comparing the effects of feeding larvae with copepod nauplii/ copepodites and rotifers. This article reports the results of these feeding protocols on the growth, survival and morphological development of orange-spotted grouper larvae. Effect of Two Zooplankton Feeding Regimens on Development of Early Larval Stages of Orange-Spotted Grouper Omer M. Yousif, K. Krishnakumar, V. Balamurgan and Hozifa A. Sagir FIGURE 1. Larval body length variations under the two feeding regimes. FIGURE 2. Larval weight distribution at first grading on 40 dph. (CONTINUED ON PAGE 38)
RkJQdWJsaXNoZXIy MjExNDY=