Plant diet tastes more to fish closer to equator. Temperature is the reason
The number of herbivorous fish decreases with increasing latitude. At higher latitudes, fish consuming plant matter are exclusively omnivorous.
We assessed whether omnivorous fish readily shift to herbivory or whether animal prey is typically preferred. Preferences of omnivorous fish for animal vs. plant diet are driven by temperature (see graph). In the mesocosm experiment with rudd (Scardinius erythrophthalmus) as a model organism, we offered them animal and plant diet in three different ratios 1:1 (grey), 1:10 (blue), 1:400 (green) under three different temperatures (16, 20 a 24 °C). Plant matter was mainly preferred under the highest temperature with the highest amount of offered plants. Decreasing plant matter and increasing animal prey led to a decrease in observed herbivory. Rudd essentially consumed only animal prey at the lowest temperature in all three experimental concentrations because low temperature inactivates enzyme cellulase responsible for cellulose digestion.
Therefore, we addressed temperature as the key factor causing absence of herbivorous fish at higher latitudes and discuss their potential poleward dispersion caused by climate changes.
More details may be found in the following publication:
Vejříková I., Vejřík L., Syväranta J., Kiljunen M., Čech M., Blabolil P., Vašek M., Sajdlová Z., Chung S., Šmejkal M., Frouzová J., Peterka J. (2016). Distribution of herbivorous fish is frozen by low temperature. Scientific Reports 6. doi: 10.1038/srep39600.