Comparative Analysis of Commercial Feeds for Brook Trout Fingerlings. James Barron Abstract Lake Superior strain brook trout were put into 3 different tanks. Each tank was fed a different feed for a 6 week period to determine which feed provides optimal growth and health of the fish without compromising water quality. Each feed is different in protein and fat content as well as cost. The three feeds used in the experiment were Silver Cup Salmon diet, Silver Cup Steelhead diet and Purina Aquamax. The Silver Cup Salmon diet provided the highest weight gain in the trout. Silver Cup Steelhead diet provided the highest length gain in the trout but only by a slight amount more than the Silver Cup Salmon diet. Purina Aquamax was found to result in lower nitrates and ammonia in the effluent water than the other diets. Introduction When raising brook trout there are several feed options to choose from at any given stage of their growth. Feed cost is an important factor when selecting a feed; however it may be out weighed by nutritional value to the fish and the resulting growth rates. A trout farmer should make an educated decision as to what feed to use based on price, protein and fat content. Fat and protein are essential for fish growth so it may seem advantageous to have the highest levels of fat and protein possible in a feed as weight gain is considered to be the most important indicator of marketability (Royes 2005). When looking at growth it is important to consider not only how long the fish are getting but also how robust they are and this is often characterized by condition factor; defined as the nutritional state or well-being of an individual fish (Henne 2006). However, the drawbacks to high fat, high protein diets often include increased cost and increased water fouling by nitrogenous waste (Royes 2005). The goal of this study was to determine the benefits of some of the available commercial feeds when raising coaster brook trout by examining growth, water quality, and feed costs. The three diets compared were Silver Cup Salmon diet, Silver Cup Steelhead diet and Purina Aquamax Starter Fingerling 300 diet.
Methods Three 4 x 1 foot circular fiberglass tank inserts were used for the experiment. Each tank has a 100 gallon capacity. Foam insulation was siliconed into the square drain opening on the tanks. A 2 PVC stand pipe rose up 5.5 through the middle of the foam insulation in each tank and silicone was put around it to seal it, this pipe acted as the stand pipe. A plastic mesh was attached to the stand pipe to prevent fish from escaping. Each tank holds approximately 50 gallons of water when filled to the stand pipe and is a flow through design. Fresh water is delivered through an inlet drilled in the 1 PVC down pipes, with a flow control valve for each tank. Tanks were set at equal flow rates at a level comfortable for the fish. Each tank was fitted with a cover made from foam insulation that covered the entire tank to prevent excessive light exposure, with an opening cut in the foam top for the belt feeders. 100 Lake Superior strain brook trout were weighed and measured initially and put into each tank. These fish averaged 73 mm in length and 3.6 g in weight at the beginning of the experiment. They were being fed Silver Cup Salmon 1.0 mm before the experiment began. Tank 1 was fed Silver Cup Salmon diet 1mm until day 10 of the experiment when the Silver Cup Steelhead 1.5mm arrived, from day 10 on they were fed Silver Cup Steelhead 1.5 mm. Tank 2 was fed Silver Cup Salmon diet 1.0 mm initially then on day 16 of the experiment Silver Cup Salmon 2.0 mm was mixed with the 1.0 mm at a ratio of 1:1 by volume to make feed sizes more equal and appropriate for the fish. Tank 3 was fed Purina Aquamax Starter Fingerling 300 for the duration of the experiment. Protein and fat contents of the diets can be found in Table 1. The fish were all fed at 5% of their total body weight per day. For the first week of the experiment the fish were hand fed throughout the day, but were put on belt feeders after a week and fed continuously during the day for approximately 8 hours. Small squares of Styrofoam were floated and suspended at a slight angle under the belt feeders to help distribute the feed across the water s surface, as the fry seemed to prefer feeding from the surface and appeared to consume more of their food when fed this way. The tanks were cleaned by siphoning each morning and each night after all of their feed had been fed for the day. Sample counts of 20 fish were taken weekly from each tank and feed adjustments were
made weekly. The fish were always fasted before the sample counts. Daily water monitoring (Table 4) included temperature, dissolved oxygen, total dissolved gasses and ph. Gas and temperature levels were monitored using the Total Dissolved Gas Monitor produced by Common Sensing Inc model # TBO-DL6F. ph was read using a Pinpoint ph probe by American Marine Inc. Nitrate and ammonia levels of the effluents from each tank were measured twice during the experiment at mid-day or approximately 3 hours after the previous feeding (Table 3). Incoming water was also tested for nitrates and ammonia to find a baseline value using a Hach test kit model CEL 850. The scale used for sample counts and weighing daily rations was the Accu-weight by Yamato model# PPC-200W. The Belt feeders that were used were made by Ziegler Brothers Inc. Length and average mass (weight) were analyzed using linear regression analysis by date with the correlation coefficient (R 2 ) and equation for the regression line indicated for each feed type. Water quality data (temperature, ph, dissolved oxygen, and total dissolved gases) were reported daily and condition factor (CF = W/L 3 ) was reported for each weekly sample. Results The fish fed Silver Cup Salmon diet yielded the highest weight gain (Figure 1) and the highest growth rate by weight. Purina Aquamax yielded the lowest total weight gain; however, the lowest growth rate by weight was seen in the trout fed Silver Cup Steelhead diet. Silver Cup Steelhead diet yielded the highest gain in length (Figure 2) and growth rate by length however it performed only slightly better in respect to length than the Silver Cup Salmon diet. Purina Aquamax had the lowest gain in total length and the lowest growth rate by length (Table 2). Linear regression analysis of both length and weight showed significant increases in length (p < 0.001, F = 642.18, df = 5, R 2 = 0.9938) and weight (p < 0.001, F = 466.57, df = 5, R 2 = 0.9915) for brook trout fed the Silver Cup Steelhead diet. Significant increases in length (p < 0.001, F = 1136.24, df = 5, R 2 = 0.9965) and weight (p < 0.001, F = 80.97, df = 5, R 2 = 0.9529) were also seen in brook trout fed Silver Cup Salmon diet and in length (p < 0.001, F = 161.74, df = 5, R 2 = 0.9759) and weight (p < 0.001, F = 95.43, df = 5, R 2 = 0.9598) for brook trout fed Purina Aquamax.
For effluent ammonia levels, the tank fed Silver Cup Salmon had the highest levels on both dates of testing. Silver Cup Steelhead and Purina Aquamax both had equally low ammonia readings (Table 3). Effluent nitrates were highest for the Silver Cup Salmon diet on the first date, but highest for Silver Cup Steelhead on the second date. Purina Aquamax had the lowest nitrites on both dates (Table 3). Condition factor ranged from 9.326E-06 to 9.933E-06 for the Silver Cup Steelhead diet. From 9.005E-06 to 1.059E-05 for the Silver Cup Salmon diet and from 8.823E-06 to 1.024E-05 for Purina Aquamax (Table 4). Temperature Ranged from 7.7-9.0(C) in the Silver Cup Steelhead tank (Table 5). In the Silver Cup Salmon tank temperature ranged from 7.6-9.0 o C. In the Purina Aquamax tank the temperature ranged from 7.6-9.0 o C. In the Silver Cup Steelhead tank Ph ranged from 7.82 to 8.58. In the Silver Cup Salmon tank ph ranged from 7.81-8.54. In the Purina Aquamax tank ph ranged from 7.81-8.58. In the Silver Cup Steelhead tank dissolved oxygen ranged from 10.61-11.64 ppm. In the Silver Cup Salmon tank dissolved oxygen ranged from 10.34-11.67 ppm. In the Purina Aquamax tank dissolved oxygen ranged from 10.36-11.34 ppm. For total dissolved gas pressure in the Silver Cup Steelhead tank a range of 692-759 mmhg was observed. For the Silver Cup Salmon tank total dissolved gas pressure ranged 706-756 mmhg. For the Purina Aquamax tank total dissolved gasses ranged from 715-750 mmhg (Table 5). There were no mortalities during the experiment. Discussion Each of the three feeds had advantages and disadvantages. For growth, Silver Cup Salmon diet seemed to be the most effective. This is not surprising since the main difference in the Silver Cup Salmon diet is the higher fat content when compared to the other two feeds. While a high fat diet may lead to large gains in growth, these levels of fat in the food tend to produce more nitrogenous waste, and unless the system where the fish are housed is capable of lowering nitrites and ammonia to safe levels, fish stress and mortality could possible result. The Silver Cup Steelhead diet caused the fish to grow better in length than the other feeds. This cannot be due simply to levels of protein or fat, since the steelhead diet
has the lowest values of both compared to the other feeds unless it was the lower fat and protein content that lead to a more slender growth pattern. Perhaps a blend of the steelhead diet and the salmon diet would provide even better growth in respect to length and weight than either of the feeds alone. The Purina Aquamax diet did not produce better length gain than either of the two Silver Cup diets, but it did fair in respect to weight gain. This diet contained the highest composition of protein, but this did not seem to have any profound effect on promoting fish growth. The tank fed Purina Aquamax had the cleanest water in respect to nitrites and ammonia, but levels for ammonia were equal to that of the Silver Cup Steelhead tank, indicating a possible correlation between the lower fat content of these two diets to lower ammonia levels in the water. If water fouling issues are a concern Purina Aquamax may be a good choice. Purina Aquamax had the lowest price per pound, however I found feed costs can be highly variable dependant on the volume purchased. The results may also have been affected by the differences in the size of the feeds. Silver Cup Salmon was in 1 and 2 mm sizes, so I created a blend of the two sizes to try to make the feeds being compared as equal as possible. Silver Cup Steelhead was in 1.5mm. Purina Aquamax fingerling 300 was around 1.4mm. Fish size was appropriate based on the manufacturers recommendations for all of these feeds throughout the experiment. Factors not measured in this pilot study included flavor and palatability. Both factors could have influenced the feeding rate and growth of the fry and should be included in future studies. Another issue arose in the initial collection of these fish from their original tank. Some of the fish were collected, after being fasted for the morning. All of these fish were weighed and measured. The automated feeders on the tanks of origin then proceeded to go off during the collection, causing the remaining fish to have bellies full of food, thus causing their weight to be higher initially, which would have led to a more significant weight change in the fish that were fasting. To correct this issue, I omitted the all of the weights from the initial collection however the initial lengths were still relevant and thus included. Acknowledgements
I would like to thank the University of Wisconsin Stevens Point Northern Aquaculture Demonstration Facility (NADF) for providing me with the resources to run this experiment. I would like to thank Greg Fischer and all of the NADF employees who helped me design, set up and run this experiment. I would like to thank Dr. Chris Hartleb for his assistance and input on this project.
Table 1: Critical properties of the selected feeds. Feed Size Used Protein (%) Fat (%) Estimated Cost ($/lb) (mm) Silver Cup Steelhead diet 1.5 45 16 0.385 Silver Cup Salmon diet 1 and 2 45 19 0.385 Purina Aquamax Starter Fingerling 300 1.4 50 16 0.32 Table 2: Changes in length and weight from the start of the experiment to the end. Tank Silver Cup Steelhead Silver Cup Salmon Purina Aquamax total weight gain (g) 3.13 3.42 2.97 total % growth by weight 74.52 81.42 75.19 total Length Gain (mm) 17.36 17.33 16.13 total % Growth by length 23.63 23.43 22.1 Table 3: Displays effluent and baseline readings from the experiment. Baseline values are the recorded values from the fresh water entering the systems. tank date Nitrite ppm Ammonia ppm Silver Cup Steelhead 7/26/2006 0.005 0.01 8/15/2006 0.006 0 Silver Cup Salmon 7/26/2006 0.007 0.08 8/15/2006 0.005 0.02 Purina 7/26/2006 0.001 0.01 8/15/2006 0.001 0 Baseline 0.006 0 Table 4: Weekly condition factor of the brook trout fry (the >CF the more weight per unit length). Date Silver Cup Steelhead Silver Cup Salmon Purina Aquamax July 18 0.0000093 0.0000090 0.0000088 July 25 0.0000096 0.0000093 0.0000090 August 1 0.0000099 0.0000106 0.0000102 August 8 0.0000099 0.0000098 0.0000093 August 15 0.0000098 0.0000100 0.0000098
Table 5: Water quality variables during the experiment. Date Temperature (C) ph Silver Silver Silver Cup Cup Purina Cup Steelhead Salmon Aquamax Steelhead Silver Cup Salmon Purina Aquamax DO (ppm) Silver Cup Steelhead Silver Cup Salmon Purina Aquamax TDGP (mmhg) Silver Silver Cup Cup Steelhead Salmon Purina Aquamax 10-Jul 8.4 8.3 8.3 7.93 8.07 8.07 10.93 10.99 10.81 748 744 743 11-Jul 7.9 8 8.1 8.07 8.03 7.95 10.91 10.51 11.09 728 738 742 12-Jul 8.1 8.1 7.7 8.15 8.12 8.11 11.09 11.14 11.34 751 750 747 13-Jul 7.7 7.6 7.6 8.02 8.06 8.07 11.19 11.22 11.14 718 726 729 14-Jul 8.1 8 8 8.05 8.09 8.11 11.01 11.04 10.89 713 720 725 16-Jul 8 8 8 7.82 7.81 7.81 17-Jul 9 9 9 8.04 8.03 8.04 18-Jul 8.5 8.5 8.5 8.33 8.28 8.28 19-Jul 7.9 7.9 7.9 8.26 8.2 8.21 11.64 11.67 11.29 737 743 745 20-Jul 8.5 8.4 8.4 8.41 8.35 8.34 10.93 10.81 11.08 741 742 743 21-Jul 8.3 8.3 8.3 8.17 8.24 8.25 11.18 11.26 11.18 735 738 742 22-Jul 8.4 8.3 8.4 8.16 8.22 8.24 10.71 11.1 11.16 759 741 743 23-Jul 8.4 8.3 8.4 8.27 8.27 8.27 10.93 11.18 10.96 24-Jul 8.5 8.4 8.5 8.02 8.12 8.17 10.76 10.71 10.46 717 724 728 25-Jul 8.1 8 8 8.3 8.26 8.25 10.94 11.34 11.19 723 724 725 26-Jul 8 8 8 8.37 8.37 8.35 10.96 11.29 11.29 723 723 725 27-Jul 8.1 8 8.1 8.08 8.13 8.17 11.16 11.24 11.09 720 723 727 28-Jul 8.2 8.2 8.1 8.58 8.51 8.48 11.36 11.21 11.01 740 740 739 29-Jul 8.1 8 8 7.99 8.04 8.14 10.89 10.6 10.89 692 706 713 30-Jul 8 7.9 7.9 8.42 8.36 8.35 10.91 11.06 10.84 729 728 728 31-Jul 8.4 8.4 8.4 8.51 8.43 8.42 11.01 11.08 11.08 719 719 721 1-Aug 8.4 8.3 8.3 8.31 8.31 8.31 11.01 10.96 11.04 742 742 742 2-Aug 8.2 8.2 8.2 8.17 8.22 8.23 10.74 10.91 10.54 726 731 732 3-Aug 8.3 8.2 8.2 8.16 8.21 8.24 10.84 10.91 11.06 725 728 730 4-Aug 8.3 8.3 8.4 8.14 8.18 8.2 10.74 11.08 11.04 734 736 738 5-Aug 8.3 8.3 8.3 8.31 8.33 8.34 10.74 11.11 11.11 741 741 742 6-Aug 8.3 8.3 8.3 8.48 8.43 8.43 10.96 10.96 10.89 7-Aug 8.3 8.3 8.3 8.16 8.2 8.22 10.66 10.89 10.89 735 756 738 8-Aug 8 8.1 8 8.15 8.18 8.22 10.89 10.71 10.96 738 746 750 9-Aug 8.3 8.3 8.3 8.57 8.52 8.48 10.81 10.89 10.61 733 738 741 10-Aug 8.2 8.2 8.2 8.21 8.17 8.12 10.89 10.84 10.76 732 735 739 11-Aug 8 8.1 8 8.5 8.54 8.58 10.74 10.56 10.74 735 732 732 12-Aug 8.2 8.1 8.1 8.33 8.28 8.3 10.64 10.49 10.49 726 734 738 13-Aug 8.4 8.4 8.4 8.23 8.27 8.32 10.64 10.71 10.36 733 729 726 14-Aug 8.2 8.2 8.2 8.26 8.28 8.26 10.61 10.69 10.69 725 729 732 15-Aug 8.1 8.1 8.1 7.84 7.87 7.9 10.64 10.34 10.56 713 720 725
Average Length(mm) Average Mass (g) 8 7.5 7 6.5 6 5.5 5 4.5 4 y = 0.1211x - 4709.5 R 2 = 0.986 y = 0.1255x - 4880.1 R 2 = 0.9566 y = 0.1155x - 4492.7 R 2 = 0.9865 3.5 7/17/2006 7/22/2006 7/27/2006 8/1/2006 8/6/2006 8/11/2006 8/16/2006 8/21/2006 Date Silver Cup Steelhead Silver Cup Salmon Purina Figure 1: Changes in weight of the fry in each tank for the duration of the experiment (Data from the first sampling date were omitted since the fish were recently fed and fish weight was inflated). 95 90 85 80 75 Silver Cup Steelhead Silver Cup Salmon y = 0.5214x - 20214 R 2 = 0.9938 y = 0.4911x - 19035 R 2 = 0.9965 y = 0.4882x - 18921 R 2 = 0.9759 70 7/7/2006 7/12/2006 7/17/2006 7/22/2006 7/27/2006 8/1/2006 8/6/2006 8/11/2006 8/16/2006 8/21/2006 Date Purina Figure 2: Changes in length during the experiment.
Works Cited Henne J. P., et al. 2006. Performance of Endangered Bonytails Fed Four Commercial Diets. North American Journal of Aquaculture 68:217-223. Royes, J. A. B., D. J. Murie. 2005. Optimum Dietary Protein Level for Growth and Protein Efficiency without Hepatocyte Changes in Juvenile African Cichlids Pseudotropheus scolofi. North American Journal of Aquaculture 67:102-110.