32 SEPTEMBER 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Environmental Technologies (University of Maryland, Baltimore, MD, USA). To assess male black snook maturation, gentle pressure was applied lengthwise to the abdomen below the testes to assess the presence of flowing milt (Fig. 8). If no milt was obtained, a cannulation biopsy was performed with a 5 fr tube using the procedures described for females to check for milt and determine if the male had undergone sex reversal to a female. No hormone therapy was used for males. When the evaluation was complete, each fish was revived to the point where it could maintain buoyancy and then returned to the broodstock holding system. Tank water level was increased to full volume and fish were allowed to spawn volitionally. Egg Collection and Egg Quality Assessment A skimmer bar on the tank surface was used to direct eggs into an external collection tank containing a 300-μm Nitex® mesh bag. After 24 hours, monitoring of the bag and tank for eggs was initiated, checking both every 2 hours. The 2-hr window between observations was used to reduce potential impacts on spawning or courtship behavior. After a spawn was observed, we continued to monitor the egg collection tank by sieving 9 L of water from the tank every hour to determine when all eggs had been harvested. After all eggs were harvested from the tank, the collector was removed and emptied to assess fertilization rate and spawn volume. Harvested eggs were added to a graduated Artemia hatching cone that was filled to a known volume and gently aerated. When eggs reached at least the blastula stage (approximately 4-5 hr post-fertilization), spawn quality and fertilization rate was assessed. Assessment was carried out by increasing aeration in the hatching cone to a more vigorous level to mix eggs evenly in the cone. Three 10-mL aliquots were collected, aeration returned to a normal, gentle level and every egg in each sample counted to determine the number of eggs/ml in the Artemia cone and estimate the spawn size. Fertilized and unfertilized eggs were counted separately to determine fertilization rate. Following the spawn assessment, aeration was removed, allowing non-viable eggs to settle to the bottom of the cone and discarded. The remaining floating fertilized eggs were removed for cleaning by draining through a 500-μm sieve. Eggs were rinsed in three separate buckets containing approximately 6 L of clean full-strength seawater, and moved to a clean hatching cone for distribution to larval tanks. The broodstock spawned twice (24 and 48 hr) following the June and July sampling events (Table 1). More than 2.5 million eggs (more than 1.2 million fertilized) were collected from the June and July spawns with an overall fertilization rate of 47 percent and mean hatch rate of 96 percent. The second spawn in July was not fertilized, so it was not included in the reported mean hatch rates. At 28 C, black snook eggs (Fig. 9) develop at nearly the same rate as common snook eggs (Yanes-Roca et al. 2012) TABLE 1. Spawning data collected on black snook at Mote. Sampling Date Spawning Date Total Number Fertilization Rate (%) Hatch Rate (%) 6/4/2014 6/5/2014 1,339,033 50.9 96.6 6/6/2014 188,700 45.1 94.5 7/16/2014 7/17/2014 834,700 51.9 95.9 7/18/2014 177,233 0.0 n/a FIGURE 7. Cannulation biopsy performed on a female black snook to assess oocyte maturation. FIGURE 8. Applying gentle pressure to the abdomen of a male black snook to express milt.
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