The influence of fish on leaf breakdown in a Virginia pond

1. To find if fish affect leaf breakdown, sugar maple leaves ( Acer sacchrum March) were placed in a soft-water, farm pond at a depth of 1 m for up to 3 months in four treatment groups: (1) enclosure with sunfish (Lepomis macrochirus Rafinesque) (SUNFISH treatment); (2) enclosure with catfish ( Ictalurus punctatus Rafinesque) (CATFISH treatment); (3) enclosure without fish (NO FISH treatment); and (4) no enclosure (OPEN treatment). The study was conducted in spring and autumn.
2. The leaf breakdown rates, k ±95% CL, for SUNFISH (0.0082± 0.00059 and 0.0111±0.00162 d⁻¹) and CATFISH (0.0072±0.00096 and 0.0103±0.00077 d⁻¹) were greater in spring and summer, respectively, than in the OPEN treatments (0.0065 ±0.00048 and 0.0105± 0.00141 d⁻¹) and NO FISH (0.0067±0.00039 and 0.0088±0.00099 d⁻¹). However, only k for SUNFISH was significantly different from NO FISH and OPEN treatments.
3. Fish in the pond did not appear to affect breakdown rates of OPEN leaf packs in the first replicate but k approached that of the fish treatments in the second replicate.
4. Fish may have promoted leaf breakdown directly by fragmentation of leaves while foraging for food and, indirectly, by agitation of leaves, leading to increased microbial activity.