World Aquaculture September 2018

WWW.WA S.ORG • WORLD AQUACULTURE • SEP TEMBER 2018 49 ( C O N T I N U E D O N P A G E 5 0 ) aquaculture (Oesterling et al . 2004, Ohs et al . 2013) was available, but details about spawning and rearing has been lacking. Recent research findings on captive spawning (DiMaggio et al . 2013) and fingerling production in indoor aquaculture systems (Oberg et al . 2014, DiMaggio et al . 2014, Faulk et al . 2018) indicate that this species has great promise for commercial production. Here we provide general observations on broodstock husbandry obtained over the last six years and a detailed protocol for obtaining volitional spawns outside of the natural spawning season using photothermal manipulations. We also describe the effects of sudden changes in temperature and salinity on survival of juvenile pigfish to assess the feasibility of moving fingerling production from indoor facilities to outdoor ponds for commercial-scale production. Broodstock and Spawning In January 2012, 11 adult pigfish ranging in size from 180-220 mm total length (TL) and 150 to 250 g wet weight (WW) were collected by hook and line near offshore oil and gas platforms near Port Aransas, TX, USA (Fig. 3). Water depth was approximately 15 to 20 m and all fish were caught near the bottom of the structure during a single trip. Pigfish apparently form spawning aggregations at this type of structure during January and February in the Gulf of Mexico near Texas, as we have collected dozens of mature pigfish each year using this method. Many of the fish caught were sexually mature, with eggs or milt flowing when gentle pressure was applied. Pigfish were transported to shore in a live well or ice chest with supplemental oxygen and placed into a recirculating aquaculture system consisting of a round fiberglass tank (3.0 m diameter, 1.4 m deep) connected to a biofilter, sand filter and heat pump. Tank effluent flowed through a 3 in (7.5 cm) diameter PVC pipe, which drewwater from near the tank surface to facilitate egg collection, into a 500-µmmesh bag attached to the inflow pipe of the biofilter. The photoperiod for the tank systemwas adjusted to 10 h light: 14 h dark and the water temperature was adjusted to 20 C to simulate conditions during the natural spawning season, and the salinity was 30-35 g/L. Fish were offered small pieces of previously frozen shrimp, squid and sardines during the first few days but did not actively feed until one week after capture. Once they began feeding well, broodstock were fed once daily and were observed feeding voraciously. Pigfish are naturally skittish, so structures made of bundles of 4 in (10 cm) diameter PVC pipe were placed in the center of the tank to provide shelter and reduce stress. Fish tended to form a compact school or remained inside or near the structure provided, especially during the first two weeks of captivity. Eggs were first collected approximately one month after cap- ture and 16 natural spawns occurred over the next 34 days. Spawn sizes ranged from 2,200-110,000 floating, viable eggs. Mean egg diameter measured from five spawns ranged from 0.76-0.81 mm, with an estimated 2,200 eggs/mL, and hatching rates ranged from 63-93 percent. Al- though environmental conditions were held constant, spawning ceased on 2 April after which the process of photothermal cycling the fish for the next spawning season began. Photoperiod and water temperature were changed by one hour of daylight and 1 C every four weeks. This schedule took the fish to 25 C and 14 h of light and then to 20 C and 10 h of light over the next eight months (Fig. 4). This group of fish resumed spawning during January in 2013 and 2014. After the initial success of naturally spawned wild pigfish in 2012, FAML staff have collected wild broodstock each year since in an effort to cycle several tanks of fish and refine spawning techniques. In several cases, wild-caught fish began spawning much sooner, 1-14 days after collection as opposed to one month as in 2012. Broodstock tanks that contain 15-25 pigfish have produced sufficient spawns, although the exact sex ratio and number of females participating in each spawning event was not known. Adults typically spawn every 2-3 days for 2-3 months producing about 200,000 eggs per spawn. The quality of eggs varies with an average of 60 percent viable eggs and an average hatching percentage of 65 percent. The ability to control spawning and consistently produce high- quality eggs with marine finfish species is a critical component of commercial production. Following up on success with natural spawning of wild broodstock, the next step was to close the pigfish life cycle and spawn fish outside the natural spawning season. In 2013, 50 of the offspring from that year’s spawns were reared to become F1 broodstock for future use. Under the same photoperiod and water temperature regime (Fig. 4), these F1 fish matured and began naturally spawning in 2015 (two years old). The next goal was to produce eggs outside of the natural spawning season. The first attempt to do this was by shortening the refractory period to 4.5-6 months by accelerating the photothermal cycle, as has been successfully applied to other marine fishes including red drum (McCarty et al . 1986). Despite attempts with several tanks of pigfish broodstock, none spawned on the accelerated schedule. All initiated spawning at nearly the same time as fish on the normal 10-mo schedule (Fig. 5). The next attempt was to achieve out-of-season spawning by extending the refractory period (retarding the photothermal cycle). This approach was successful, producing viable spawns during the summer. The 10-mo photothermal regime was implemented at the end of July to obtain offseason spawns the following June. By shifting initiation of the photothermal regime from spring to summer, we have successfully obtained off-season spawns from four tanks of broodstock, demonstrating the ability to schedule tanks for year-round production. FIGURE 3. Collection of adult wild pigfish near an oil platform (right) and transportation back to the facility using an ice chest with supplemental oxygen (left) (Photos: Frank Ernst).