Nicole Windschanz & Sarah Barbian
††††††††††† Previous research has shown that small fish have a higher survival rate staying under cover in dark areas than venturing out into open waters.† With this said, it can be inferred that small fish forage more in darker environments to avoid predation.† This knowledge has led us to the question whether feeder goldfish (Carassius auratus) will forage more in dark areas than in light areas. Ten C. auratus were housed in a constant light environment and 10 in a constant dark environment.† Each tank was fed once daily a pre-determined mount of pellets. †It appears that C. auratus did not prefer light or dark environments in which to forage more. This finding has led us to reject our hypothesis that feeder fish will forage more in dark environments than light environments
( P > 0.05).
Small fish, especially in small shoals or alone, are the common prey to many marine and land animals.†† They are easily preyed upon due to their low numbers as a group and results in not always knowing a predator is in the area.† Larger shoals of fish defeat predation by swimming in fast, alternating directions which confuse predators and prevents a majority of them from becoming prey.† The large number of them increases the chance of detecting predators near at any given time (Magurran & Pitcher, 1982).
While searching for food, small fish are at greater risk of being prey than larger fish due to their small body size.† Having a smaller body size increases predation by many organisms of all different sizes whereas having a larger body size creates immunity against being prey to smaller predators.† It can be inferred that smaller fish will spend more of their time in cover than venture into unprotected areas.†
†One study by Werner, Mittlebach, Hall, & Gilliam (1983) states that small bluegill sunfish (Lepomis macrochirus) spent more time foraging under vegetation and in crevasses opposed to the larger bluegill who were found foraging mostly in open waters.†† Smaller bluegill used the protection of weeds and crevasses provided to conceal themselves from predators in these areas.†† Vegetation areas were more profitable to the small bluegill than open water areas.† Profitability, in this case, means there was more food available under vegetation and a lesser risk for predation (Werner, Mittlebach, Hall, & Gilliam, 1983).†
Since small fish are taking refuge under vegetation and in crevasses, the amount of sunlight available is less than in areas of open water.† Open water areas donít have anything to block sunlight so visibility is more clear and brighter than in covered areas.†† The preceding findings have led us to assemble an experiment that tests how the impact of light in an environment has on the foraging of feeder goldfish (Carassius auratus).† †We hypothesized that C. auratus will forage more in a constant dark environment than in a constant light environment.
The twenty-six Carassius auratus that were obtained from Pet World Warehouse Outlet store were randomly chosen from a pre-existing environment by a store employee prior to purchase.† After purchase twenty fish were equally divided into 2 groups of 10, Group A and Group B.† Each group was housed in one 10 gallon rectangular tank (50.8 cm x 30.5 cm x 25.4 cm) with an air bubbler for oxygen.† The remaining 6 were split and equally placed into 2 other smaller holding tanks (size of tanks is not a factor) each with a bubbler.† These extra fish were used to replace fish that died during the experiment.† Each tank was treated with Start Right aquarium treatment prior to housing.
†Group A, along with a holding tank, was placed into a room that is completely dark 24 hours each day and Group B, also with a holding tank, was placed into a room that was lit by an overhead light 24 hours each day.† Group A was under a 60 watt ZooMed nightlight red reptile bulb for easier visibility of the subjects during testing.† Each group was habituated to their new environments for 48 hours prior to testing.† Four times during this 48 hour period, we fed each tank simultaneously 25 Wardley Floating Goldfish Pellets and counted the eaten pellets after a 5 minute period.† The number of eaten pellets at each feeding accounted for the maximum number of pellets each group is able to eat within 5 minutes.† The maximum number of pellets eaten by each group were recorded and averaged.† The average maximum number of pellets eaten by both groups was 16.5.† The fish were not fed 24 hours prior to the first test day to ensure hunger.
Recordings were done between the hours of 12:00pm and 1:00pm for 7 consecutive days.† Each group was fed 17 pellets simultaneously and timed for 5 minutes. After 5 minutes the remaining pellets were counted and the number of pellets eaten was calculated.† Each group was only fed once per day to ensure hunger at the time of the next feeding. †After data was gathered an independent t-test was used to calculate the p-value to determine significance.† This experiment was one tailed because past research has lead to believe that fish forage more in dark places than in light places for increased protection and resources.
††††††††††† There was no difference between foraging environment preferences of Carassius auratus †in light versus dark environments (fig. 1, P= 0.4).†† However, the dark environment ranked higher (M=12.2, SD =2.3) than the light environment (M = 11.9, SD = 1.9).†
Figure 1. Environmental preference of C. auratus in relation to light and dark environments.† Error bars reflect standard deviation.††
The patterns shown by the results do not support our hypothesis that C. auratus would forage more in darker environments thank in light environments.† This could be due to the fact that they rely more on other senses such as chemoreception and electroreception and not so much on vision to hunt prey and run from predators (Jonna 2008).† Since the sensation of a light and dark environment is mostly visual, they may have paid less attention to whether the environment was light/dark and paid more attention on the sensations they were receiving via their chemoreceptors or electroreceptors.† Since the light/dark environments were exactly the same besides the light factor they may have observed the environments in the same way causing the presence or absence of light to not make a difference.† If we were to do this experiment again, we would have added plants and other characteristics of their natural to better simulate their natural home which could in turn change the way they forage.† We also would perform this experiment for a longer period of time using more individuals to get better more accurate results.
Jonna, R. (2004). Actinopterygii. Animal Diversity Web.† Accessed November 10, 2009 from http://animaldiversity.ummz.umich.edu/site/accounts/information/Actinopterygii.html.
Magurran, A.E., Pitcher, T.J., (1983).† Timidity and Shoal Size in Minnows and Goldfish.† Behavioral Ecology and Sociobiology, 12, 147-152.† Retrieved September 14, 2009 from JSTOR database.
Mittelbach, G. (1981). Efficiency and Body Size: A study of Optimal Diet and Habitat Use by Bluegills. Ecology, 62, 1370-1386. Retrieved September 14, 2009 from JSTOR database.