The moon's gravitational pull creates tidal bulges in the earth's oceans — one directly beneath the moon, and one on the opposite side of the planet. As the earth rotates, these bulges sweep across the globe, creating the roughly twice-daily tidal cycles that coastal anglers know intimately. The sun contributes about 46% of the moon's tidal force, which is why spring tides (when sun and moon align during new and full moons) produce dramatically higher highs and lower lows than neap tides (when sun and moon are at right angles during quarter moons). For saltwater fishing, the tidal connection to solunar theory is direct and undeniable. A rising tide floods grass flats, oyster bars, and mangrove shorelines, giving gamefish access to food-rich shallow habitat. Redfish follow the tide onto a flat, feed aggressively during the flood, and retreat to deeper staging areas as the water drops. The timing of this cycle is governed by the moon, and solunar tables predict it accurately. This isn't mystical — it's hydrodynamics. The more controversial claim is that lunar gravity affects fish in freshwater, where there are no meaningful tides. Knight's theory proposed that the gravitational effect operates directly on organisms, not through tidal movement — that the same force that moves oceans also triggers behavioral changes in animals, including inland fish. Some studies have shown correlations between lunar position and freshwater fish activity, but the effect sizes are small and inconsistent. The gravitational differential between the moon directly overhead and the moon at the horizon is about 0.00003% of surface gravity — far less than the pressure change from a fish swimming up or down a foot in the water column. Light is a more plausible mechanism for freshwater lunar effects. Full moon nights provide significantly more ambient light than new moon nights, which affects nocturnal feeding behavior in documented ways. Freshwater predators like brown trout and smallmouth bass feed more actively on bright moonlit nights, likely because the increased light improves their visual hunting efficiency. This is a real effect, but it's driven by moonlight, not gravity.

The peer-reviewed literature on solunar theory is a mixed bag, which is itself informative. Several studies on largemouth bass in freshwater lakes found no statistically significant correlation between solunar periods and catch rates. A Texas Parks and Wildlife study analyzing thousands of largemouth bass catches found no relationship between moon position and feeding activity. These freshwater null results are the strongest argument against solunar theory as a universal principle. However, studies on coastal and marine species tell a different story. Research on red drum (redfish) in the Gulf of Mexico found strong correlations between tidal phase and feeding activity, which is effectively a validation of solunar timing since tides are the physical manifestation of the forces solunar tables predict. Studies on tarpon migration in Florida showed that major migratory pushes corresponded to new and full moon periods. Bonefish feeding activity on Bahamian flats was significantly higher during moving tides than during slack water. The reconciliation is straightforward: solunar theory works where tides matter. In tidal environments, the moon controls water movement, water movement controls forage distribution, and forage distribution controls when and where gamefish feed. The chain of causation is clear and physical. In freshwater, where tides are negligible, the proposed mechanism — direct gravitational influence on fish biology — is too weak to produce a measurable behavioral effect against the noise of other variables. The practical takeaway: if you fish salt, use solunar/tidal data as a primary planning tool. If you fish fresh, use it as a minor consideration at best, and invest your analytical energy in temperature, flow, and weather instead.