The effects of water temperature on feeding behavior in the guppy, Poecilia reticulata.
Rosie Berger and Jessica De Santis
Alverno College 2009
We tested the effect of increased water temperature on the feeding behavior of the guppy, Poecilia reticulata. We found that increasing the water temperature from 21oC to 28oC increased the rate at which the guppies fed. A t-test produced a P-value of 3.0 x 10-4, showing that our results are statistically significant and not by random chance. The guppies did show a higher foraging rate in the warmer water temperatures.
Keywords: guppy foraging, Poecilia reticulata, feeding rate, water temperature
Guppies are generally found in warmer fresh waters ranging in temperatures from 20-28oC. Changes in water temperature have been observed to affect the feeding behavior of the fish; in higher temperatures guppies have been observed showing an increase in their foraging behavior (Weetman et al, 1998). It has been shown that guppies in lower temperatures possess more unsaturation in their fatty acids than those in higher temperatures (Knipprath & Mead, 1965). Higher unsaturated fatty acids in the fish will cause them to be more fluid in movement, which may cause more movement by the fish and therefore higher foraging rates. This would refute our hypothesis, but there is a more likely reason for warmer temperatures affecting foraging rates. Guppies are an ectothermic animal, which means that their enzymatic metabolism is reliant on external heat sources. Enzymes also have an optimum temperature to function, so it is also assumed that an increase in water temperature to the highest temperature guppies would naturally live in (28oC) will increase the foraging rates of the guppies.
Higher temperatures have also been shown to increase the shoaling (schooling) behaviors of guppies, which can also increase their foraging behaviors due to an increase of protection from predators (Weetman et al, 1999). Predators are more likely to attack single fish than large schooling groups (Magurran, 1990). Guppies have also been known to learn feeding behaviors when presented with a certain schedule; guppies will feed much quicker after not being fed for a certain time period than if they are fed frequently (Reader & Laland, 1999). Our hypothesis was that the guppies would feed at a faster rate in warmer water.
Three 4 L aquariums were filled to the brim with room temperature water and treated with NovaAquaÓ water conditioner. Aerators were placed in the water to ensure the guppies had a plentiful oxygen supply and water circulation. No gravel or plants were placed in the tanks. Each tank was labeled as Tank A, Tank B or Tank C. Tank A was kept at room temperature that varied from 21oC to 22oC, but was most often 21oC. Tank B was supplied with a 25 Watt Slim-TechÓ aquarium heater and varied from 27 oC to 30 oC, but was most often 28oC. Tank C temperature was not measured, since these guppies were not being tested, but kept at room temperature and was only used to keep replacement guppies in case of guppy deaths in Tanks A or B. Tank A and Tank B were each supplied with 10 female guppies, and Tank C was supplied with 7 female guppies. The temperatures of Tank A and Tank B were measured using an Aqua CultureÓ digital fish tank thermometer.
For six days, the guppies were fed twice daily, once in the morning before , and once in the evening after . During each feeding the guppies were given 0.02 gm of TetraFinÓ colored goldfish flakes, which were crushed small enough for easy consumption. The guppies were observed for 10 minutes and the feeding rate was determined by a stopwatch. Once all food was consumed from the tank, the timing was stopped and recorded. If the guppies did not finish all of the food given, the timing was stopped at 10 minutes and this was recorded as the feeding time.
Tanks A and B were consistently supplied with 10 guppies each. A third tank, Tank C, was set up and supplied with 7 guppies to use as replacements if any guppies in Tank A or Tank B died. This would ensure that there was always the same number of guppies in each tank being measured. If a guppy died, it was recorded and replaced before feeding. To determine statistical significance, a type 1, paired, t-test was performed using Microsoft Excel 2003. This information gave us our P-value.
We found that there was a clear difference in feeding rates of guppies depending on water temperature (Fig 1, P<0.0003). Guppies in water of 28oC, Tank B, had a faster average feeding rate than guppies in water of 21oC, Tank A (Tank B: Mean=78.0, S.D.=44.4). Guppies in Tank A fed slower than guppies in Tank B (Tank A: Mean=391.25, S.D.=234.5). The guppies in Tank B appeared to swim faster and move more often than those in Tank A.
Fig 1: Feeding time (Mean +/- SD) of guppies (s) to eat 0.02 g of food with a maximum of 10 minutes time dependant on water temperature (P<0.0003). Tank A represents guppies in 21oC water and Tank B represents guppies in 28oC water.
During the first few feedings in this study the tank temperatures were not consistently 28oC and 21oC, however, the temperatures only varied slightly by +/- 2oC. After the fourth feeding the heater in Tank B adjusted to a stable temperature of 28oC and Tank A was consistent at 21oC. If this experiment were to be repeated, it would be suggested to set up the water in the tanks two days prior to supplying the guppies to obtain a stable temperature.
Guppies in this study foraged faster in 28oC water than in 21oC water. These findings supported the hypothesis that guppies would have a faster feeding rate in warmer water. The feeding times of guppies were kept consistent at twice daily, separated by even hours. This would ensure that guppies would not decrease their feeding rates since guppies feed on a schedule and may eat faster if not supplied with food for several hours (Reader & Laland, 1999).
The guppies in Tank B seemed to swim faster and more often upon observation than those in Tank A. This may be due to the guppies in Tank B having a higher metabolic rate from living in higher temperatures. Their swimming rates did not seem to be affected by a higher concentration of unsaturated fatty acids nor did there seem to be any muscle stiffening (Knipprath & Mead, 1965). Another option for their faster consumption of food could be due to an increased feeling of protection from predators, if we were observed as predators or threatening in any way, since higher temperatures increase shoaling in guppies and increased feelings of protection (Weetman et al., 1999).
Overall the hypothesis was supported. Guppies seemed to have a higher metabolic rate in warmer temperatures. This may mean that they need to consume food more often since their metabolic needs would be increased.
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Reader, S. M., & Laland, K. N. (1999) Diffusion of foraging innovations in the guppy. Animal Behaviour. 60(2), 175-180. Retrieved on April 9, 2009 from Science Direct Database.
Weetman, D., Atkinson, D., Chubb, J. C. (1998) Effects of temperature on anti-predator behaviour in the guppy, Poecilia reticulata. Animal Behaviour. 55(5), 1361-1372. Retrieved on April 4, 2009 from Science Direct.
Weetman, D., Atkinson, D., Chubb, J. C. (1999) Water temperature influences the shoaling decisions of guppies, Poecilia reticulata, under predation threat. Animal Behaviour. 58(4), 735-741. Retrieved on April 9, 2009 from Academic Elite Database.