WWW.WA S .ORG • WORLD AQUACULTURE • SEP TEMBER 2022 41 lunar phases. For this purpose, a spawning event was defined as any production of ≥10,000 eggs. There were significant difference among lunar phases. Significantly more spawning events occurred during the full moon phase than the first quarter phase, with the new moon phase having just slightly more spawns than the first quarter. The total number of eggs spawned by each tank was also calculated and the same lunar phase trend was observed (Fig. 3). Lunar Influence on Spawning Produced by the pineal gland, melatonin is important in maintaining circadian rhythms and biological clocks (Esteban et al. 2013). Changes in light levels at night were detected by fishes and this corresponded with changes in melatonin levels in fish blood (Takemura et al. 2010, Ikegami et al. 2014). Fish responded to the changes and the presence of certain hormones, such as melatonin in their bloodstream, to trigger gonadal maturation. The hypothalamuspituitary-gonad axis system of the fish responded with sex steroid hormone production resulting in gonadal development and gamete releases timed with lunar cycles (Cabrita et al. 2009, Oliveira et al. 2010). Red drum spawning was affected by lunar periodicity in controlled settings where there was a constant photoperiod and no changes in water chemistry. Red drum spawned with a direct correlation to the lunar cycles, but with no change in lunar illumination, similar to the red drum broodstock at SCT. Apparently the fish had other ways of detecting lunar phase (Celik and Celik 2011). Although lunar phases result in changes in nighttime lunar illumination, they also result in geomagnetic field fluctuations. The gravitational action of the moon causes tides in the ocean. It also caused\s periodic oscillations in the lower atmosphere (atmospheric tides) via ionospheric currents that produced a magnetic field that fluctuate with lunar phase (Stening et al. 2002). There is a decrease in geomagnetic activity by 4 percent for the seven days before a full moon and an increase by 4 percent for the seven days after a full moon. Fish capable of detecting the intensity and fluctuations in the magnetic field have an impact on the production of melatonin in some species (Nishimura and Fukushima 2009). In response to a dramatic decline in the population of red drum Sciaenops ocellatus in Texas coastal waters in the 1970s, the Texas Parks and Wildlife Department established a stock enhancement program. A fish hatchery was established in Corpus Christi with the purpose of spawning and releasing fingerlings into Texas bays (Matlock et al. 1984, McEachron et al. 1995, Vega et al. 2012). With the success of this program, Sea Center Texas (SCT) was established in Lake Jackson. In addition to red drum, both hatcheries also currently produce spotted seatrout Cynoscion nebulosus and southern flounder Paralichthys lethostigma for stock enhancement along the entire Texas coast. At SCT, the indoor recirculating aquaculture systems (RAS) that hold the red drum broodstock are manipulated with controlled photoperiods and thermal cycles to induce volitional spawning. A year of seasonal variation was compressed into a 120- to 150-d timeframe (Arnold et al. 1977, Roberts et al. 1978, McCarty 1990). Figure 1 showed red drum being taken into the beginning of their cycle that started by coming out of a rest period and was taken into winter. The cycle continues through spring and summer and begins to decline in the fall. The fall season triggered the spawning response and the fish were held at 11 hours of light for an extended period of time. Their temperature was fluctuated at controlled intervals between 24-28 C (Vega et al. 2012). To cease spawning, the temperature was dropped to 20 C and held until the next cycle began. Many factors, including moonlight, contribute to whether or not a fish would spawn at a certain time (Takemura et al. 2004, Ikegami et al. 2014). Although a large amount of control was exerted over the SCT red drum broodstock, quite a bit of fluctuation is observed in the occurrence of spawning events and the number of eggs spawned with each event. The purpose of this project was to assess the effect of lunar phase, despite a lack of change in lunar illumination in the indoor RAS, as a possible contributing factor to some of this variation. Data Review A data review was conducted for eight recent years of SCT red drum spawning data (2013-2020) (Fig. 2). The spawning events from each of 12 tanks for each year were grouped into the four Lunar Periodicity in the Spawning of Red Drum in Aquaculture Jessica Sannwaldt and Jennifer Butler ( C O N T I N U E D O N P A G E 4 2 ) FIGURE 1. Red drum photothermal cycle for 2019-2020 showing the target photoperiod, target temperature and actual temperature.
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