Raising fish in an aquarium means that there is a limit to the number of individuals that can survive in an area. For example, 700 Goldfish can't survive happily in a small fishbowl. The reason for this is that resources such as space, nutrients, dissolved oxygen and water are limited. Limited resources result in competition. Competition occurs when organisms have an adverse effect on each other as a result of requiring the same resource.
Competition occurs between two or more organisms. When these organisms belong to the same species it is referred as intraspecific competition. When it occurs between individuals of different species it is interspecific competition.
The purpose of this experiment is to examine how Goldfish compete for dissolved oxygen in an aquarium with limited resources.
Dissolved oxygen - the dissolved oxygen level in good fishing water generally averages about 9 parts per million (ppm) which are equivalent to milligrams per litre (mg/L) at 22°C (degrees Celsius). Usually, the dissolved oxygen level is affected by the temperature of water (temperature increases, dissolved oxygen decreases). In this experiment, the amount of dissolved oxygen varies according to the volume of water in the aquarium.
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Health of the goldfish - Mass and length of the goldfish.
A digital scale with an absolute error of ± 0.01 g is used to determine the initial mass of the goldfish. A ruler with an absolute error of ± 0.1 mm is used to measure the length of the goldfish (from head to tail) before placing it in the aquarium. Health of the Goldfish is affected by any factors including; the amount of dissolved oxygen in water. Under ideal conditions, the goldfish grows rapidly to its full potential size (its mass and length increases consecutively).
Goldfish in the aquarium compete for food and dissolved oxygen. Goldfish prefer living in tanks with a large surface area for optimal gas exchange. When surface area of the aquarium, amount of food, temperature of water, volume of the aquarium, number of fish and type of fish are constant; the amount of dissolved oxygen is the only independent variable. Dissolved oxygen is important for respiration process. It is related to the volume of water and the temperature of water. At constant temperature of aquatic water; water volume is the only factor that affects the amount of dissolved oxygen. In the aquarium with limited resources of dissolved oxygen, Goldfish will compete for it. Fish gasping; is related to the reduced amount of dissolved oxygen in aquatic water. Measuring the concentration of dissolved oxygen in water is a way to show how intra-specific species compete for a limited resource for respiration. When Goldfish starts gasping, it means that there is no sufficient oxygen in water. Hence, dissolved carbon dioxide level will increase by time. Wastes produced by fish including: ammonia, phosphorus, nitrate and nitrite lower the pH of water and turn it to acidic. Accumulation of wastes and the acidic pH reduce the life span of Goldfish. Therefore, partial water change should be performed weekly or twice a week to get rid of wastes and neutralize the pH. Temperature of the aquarium should be stable around 22°C - 24°C.
Null Hypothesis: In an aquarium with limited resources, there is no significant change in the health of Goldfish (mass in grams ±0.01g) caused by decreasing the concentration of dissolved oxygen in water (ppm).
Alternative Hypothesis: In an aquarium with limited resources, there is a significant change in the health of Goldfish (mass ±0.01g decreases) caused by decreasing the concentration of dissolved oxygen in water (ppm).
This test is used to compare the means of the mass of the Goldfish in different concentrations of dissolved oxygen. The P value (probability) is usually 5% or 0.05. If the P value is more than 0.05; the null hypothesis is correct. If P value is less than 0.05 (no significant change), the null hypothesis is wrong and the alternative hypothesis should be applied.
Manipulating independent variable
Volume of water is measured in Liters or Gallons. The known rule for stocking an aquarium is one inch of fish per gallon of water. The true adult size of the fish must be used in the calculations.1 US gallon = 3.78541178 liters. Dissolved oxygen is directly related to the volume of water. Generally; the dissolved oxygen level in good fishing water averages about 9 parts per million (ppm) which are equivalent to milligrams per litre (mg/L) at 22°C (degrees Celsius).
Method for recording results
Always on Time
Marked to Standard
Vernier Dissolved Oxygen Probe is used to measure the amount of dissolved oxygen in parts per million (ppm).
Scientific studies suggest that 4 -5 parts per million of dissolved oxygen is the minimum amount that will support a large fish population. The normal level of dissolved oxygen in fishing water is about 9 parts per million.
A digital scale with ±0.01g absolute error is used to measure the mass of Goldfish. The initial and the final masses for 10 Goldfish are recorded, and the mean is calculated for each aquarium. A ruler is used with ±0.1mm absolute error is used to record the length of the same 10 Goldfish in each aquarium in order to calculate the mean of the length.
Vernier Dissolved Oxygen Probe
Vernier Lab Quest Machine
5 glass aquariums with the same size and shape
50 Goldfish (adult); Comet Goldfish (reddish orange colored goldfish that are inexpensive and readily available). http://www.petworldshop.com/pictures/nitrite-test-kit.jpg
Thermometer (-10 - 100 °C)
Ruler with 1mm scalehttp://www.vernier.com/labquest/images/curriculum.jpg
Digital scale with 0.01g accuracy
Change may it cause
Size of the aquarium
Enough for fish to swim freely.
Goldfish grows rapidly, it is better to start with a big aquarium to avoid crowded aquarium
Change the amount of dissolved oxygen, and fish health
Shape of the aquarium
Long aquarium is better than tall one
Greater surface area and Better gas exchange
Change the amount of dissolved oxygen; and fish health
22 - 24 C
Increasing in temperature decreases Dissolved Oxygen
Drop in water temperature affects fish health
Amount of food and frequency per day
The same amount twice daily - 12 hrs
The same kind
Goldfish are omnivorous and eats a lot
Change the mass of fish, interferes with the results
Size, type, color, of fish
False control on fish health
Number of fish/aquarium
10 per aquarium
Fish compete for two variables, space and oxygen
Change in mass due to 2 variables
The size of the aquarium should be compatible with the number of Goldfish in. goldfish grow fast, and need a big aquarium with a large surface area for gas exchange. Thermometer is used to control the temperature of the aquatic water. A digital scale with ±0.01 g absolute is used to measure the amount of food. The number of fish depends on the size of the fish and the capacity of the aquarium. If the aquarium is too small or contains many fish; it will interfere with the studied variable and increases the percent of error. The experiment will be conducted for 7 consecutive days.
Developing a method for collection of sufficient data:
Prepare 5 glass aquariums of the same size with lids. Measure the dimensions of them and record it.
Add 30, 40, 50, 60, and 70 Liters of water to the aquariums consecutively. (rule: is one inch of fish per gallon of water) 1 US gallon = 3.78541178 liters
Use the thermometer to measure the temperature, the range is 22-24 °C.
Connect the Dissolved Oxygen Probe to the Lab Quest and measure the concentration of dissolved O2 gas in water (ppm).
Record the mass of Comet Goldfish using the digital scale and the length using the ruler.
Place 10 Comet Goldfish in each aquarium.
After one hour feed fish with the exact amount of fish food, using ±0.01g digital scale. Feed the Goldfish every 12 hours for 1 week with the exact amount of flakes each time.
Use an additional aquarium with 30 liters as a controlled one with 3 fish placed in it.
Observe the health of Comet Goldfish for 1 week. You may record any change in its color and its general health.
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Watch for fish gasping, because it is related to decreased amount of the dissolved oxygen.
Use the dissolved Oxygen Probe to measure the amount of Dissolved Oxygen. Record the measurements twice daily (every 12 hours). Make sure that the temperature is constant all of the time.
At the end of each day, measure the mass of 5Goldfish in each aquarium, and calculate the mean.
At the end of the week measure the final length of 5 Goldfish of each aquarium and calculate the mean.
Repeat this experiment three times and take the average of the measurements to decrease the percent of error. Two other groups can perform the experiments and the average of measurement can be calculated.
(Make sure that the filter of aquarium is working properly to avoid accumulation of wastes which affects the health of fish and interfere with the results).
12 hours interval
Dissolved Oxygen Concentration (ppm)
12 hours interval
Dissolved Oxygen Concentration (ppm)
The mean of mass (g) of random 5 Goldfish is measured daily.
Mass - Day 3
Mass -Day 4
Mass - Day 5
The mean of the Initial length of random 5 Goldfish is calculated for each aquarium and the final one too. It is used as an indicator for the general health and growth of the Goldfish.
Plot a graph representing the change in dissolved oxygen concentration Vs time of the 5 aquariums. If it is a linear graph, use the linear graph equation to calculate the slope (DO concentration) at any point at a certain time and b (y - intercept at zero time). Notice which aquarium has a major decrease in dissolved oxygen concentration to see how intra-specific species compete for this limited resource.
Plot another graph that represents the change in the mean of Goldfish mass (g) vs. different concentrations of dissolved oxygen (ppm). This graph will clearly show how intra specific species compete for the limited dissolved oxygen.
Ammonia, nitrate and nitrite are toxic chemicals produced in the aquarium by fish waste. Water quality test kit should be used. It contains different chemicals for testing the concentration of ammonia, nitrate, nitrite and phosphate in ppm. These chemicals threaten the life of Goldfish; it should be neutralized all the time.
Follow the animal experimentation policy which states that any planned and actual experimentation involving animals must be subject to approval following a discussion between teacher and student.
Experiments involving animals must be based on observing and measuring aspects of natural animal behavior. Any experimentation should not result in any pain or undue stress on any animal (vertebrate or invertebrate) or compromise its health in any way. Therefore experiments that administer drugs or medicines or manipulate the environment or diet beyond that easily tolerated by the animal are unacceptable. Experiments resulting in the death of any animal are unacceptable.
Be careful when performing the experiment.
Use the Lab Quest and Oxygen Dissolved Probe gently.
Aquariums should be covered to avoid causing harm to Goldfish, since it jumps most the time out of the tank.