Effect of gut passage in fish on the germination speed of aquatic and riparian plants

• Gut-passage in carp or Mozambique tilapia differently affects germination speed.
• Mastication of seeds in carp reduces germination speed of soft-seeded species.
• Stomach-passage in tilapia generally has no effect on seed germination speed.
• Variation across species in germination speed outweighed effects of gut passage.

How seed-eating animals influence the germination of endozoochorous plant species is of great relevance to our understanding of long-distance seed dispersal. To evaluate the effect of gut passage on the germination speed of aquatic and riparian plants, we fed seeds of 19 species to common carp (Cyprinus carpio) and Mozambique tilapia (Oreochromis mossambicus). Carp has a pharyngeal ‘mill’, compensating for lack of a stomach and teeth, while tilapia has tiny teeth and an acid stomach. Potamogeton species, Alisma plantago-aquatica and Sagittaria sagittifolia showed a continuous germination with relatively low, and constant germination rates throughout the germination period. In contrast, the seeds of Myriophyllum spicatum and Nymphoides peltata and those of the riparian species exhibited discontinuous germination, i.e. almost all seeds germinated within a few days. Compared to control seeds, we found on average a negative effect of gut passage on the germination speed for carp, but no effect for tilapia. However, several plant species deviated from this general pattern. For example, gut passage in carp enhanced germination speed of viable seeds relative to controls for Potamogeton alpinus, but reduced it for Filipendula ulmaria. Similarly, tilapia enhanced germination speed for P. alpinus, but reduced it for P. pusillus. We conclude that carp’s efficient mastication affects the germination speed of plant species after gut passage, whereas stomach-passage in tilapia generally does not influence the germination speed when compared to control seeds. However, inherent variation across species in germination speed proved to be greater than effects of fish gut passage.