38 JUNE 2017 • WORLD AQUACULTURE • WWW.WAS.ORG Larval Growth and Survival Larvae grew at about the same rate until 10 dph. Size variation between the two treatments occurred after 15 dph (Fig. 1). By 40 dph, larvae fed rotifers and copepods attained a body length of 28.2 ± 3.8 mm, compared to a body length of 22.6 ± 2.8 mm for larvae fed rotifers only. At harvest (40 dph), body weight ranged between less than 0.2 g to >0.4 g. After grading, the body-weight distribution of the two groups differed considerably (Fig. 2). Most (45 percent) larvae fed rotifers were <0.2 g size while most (52 percent) larvae fed rotifers and copepods were in the 0.2-0.3 g size range. Both groups had a more or less similar proportion of fish >0.3 g. Weight distribution was significantly different in the <0.2 g and 0.3 g size groups. At harvest, larvae fed rotifers and copepods had a better survival rate (9.4 ± 0.7 percent) than that of larvae fed rotifers only (4.2 ± 0.4 percent). Larval Development and Metamorphosis There was no difference between groups in metamorphic progression during early preflexion and flexion stages. The emergence of the dorsal spine bud, lengthening of the dorsal spine and the appearance of hemoglobin in the heart, notochord flexion and emergence of the third dorsal spine occurred simultaneously in both feeding regimes. However, the progression to the post-flexion stage was observed earlier in larvae fed rotifers and copepods. Larval transformation occurred over a 10-d period between 20 to 30 dph in larvae fed rotifers while this took only 5 days between 20 to 25 dph in larvae fed rotifers and copepods. By 40 dph, 90 percent of the larvae in the RC-regime group had settled and become demersal and with fully developed scales whereas only 50 percent of the larvae had settled in the R-regime group and the remaining were still in the pelagic stage (Table 1, Fig. 3a-j). Conclusions Higher growth, survival and faster metamorphosis were obtained in larvae provided with copepod nauplii and copepodites than larvae fed with rotifers alone at the onset of feeding. The results of the present larval rearing trials confirm earlier findings on the feasibility of using copepod nauplii for early-stage grouper larvae (Toledo et al. 1997, Toledo et al. 1999, Toledo 2005). Also, the progression of metamorphosis was relatively faster in the group fed copepod nauplii. Although the density of copepod nauplii provided to larvae from 2 to 5 dph in this trial (0.03-0.06 individuals/mL) and adult copepods provided to larvae from 7 to 14 dph (0.2-0.5 individuals/mL) were low, they resulted in better growth and survival rates. Results of this trial suggest that the use of pondgrown zooplankton, especially copepods, can improve hatchery production of grouper. However, fish larvae fed copepods cultured in outdoor ponds could be at risk from introduced disease problems, such as VNN and parasites. Therefore, in future trials, special attention should be given to improve production efficiency of copepods from shrimp ponds with FIGURE 3. Larval stages of Epinephelus coioides. a. b. c. d. e. f. g. h. i. j.
RkJQdWJsaXNoZXIy MjExNDY=