PALATABILITY OF FLAKE FEEDS USING THE EMPEROR TETRA

Harry Ako1, Tani Nishimura1 and Clyde S. Tamaru2

1Department of Environmental Biochemistry

College of Tropical Agriculture and Human Resources

University of Hawaii

1800 East West Road, Henke Hall, Honolulu, Hawaii 96822

2Sea Grant Extension Service, School of Ocean Earth Science and Technology

Aquaculture Development Program, Department of Land and Natural Resources

University of Hawaii

1000 Pope Road, MSB 226, Honolulu, Hawaii 96822

 

INTRODUCTION

Commercial producers of feeds for ornamental fish are continously working on improving their products. Two new flake feeds recently developed by Saunder's Brine Shrimp Company, have recently come on to the market. The company requested that we evaluate their new feeds objectively in order to assess the strengths and weaknesses of their new products. To provide an unbiased evaluation required the feeds be tested using protocols described in previous publications (I'a O Hawai'i, Vol. 1997, Issue 4, I'a O Hawai'i, Vol. 1997, Issue 5, I'a O Hawai'i, Vol. 1997, Issue 6). In this particular instance, palatability of the feeds were investigated using the emperor tetra, Nematobryon palmeri, provided to us by Mike Yamamoto an avid breeder of this particular freshwater ornamental. The results of the palatability and growth trials using these two new flake feeds form the basis for this article.

 

MATERIAL AND METHODS

The experiment was conducted in 38-liter (10 gal.) glass aquaria equipped with an airstone and constant aeration. Each tank was stocked with 33 juvenile emperor tetras each weighing approximately 185 mg and about 26 mm in body length. Three flake-feeds were investigated during the current study. Tetramin flake food was used as the industry standard to which the two new flake feeds (Tri-Flake and Black Gold) were compared. Tri-Flake is a mixture of a flake made from brine shrimp combined with several other flake feeds. Black Gold is an algal based flake feed made up of Spirulina and Schizochytrium possibly confering this flake feed with some color enhancing properties. The palatability for each of the feeds to emperor tetras was determined by the same method as described in a previously printed article (I'ao O Hawai'i, Vol. 1997, Issue 6). Fish were fed twice daily at 08:30 and 17:00 and water temperatures were observed to range between 24o C - 26o C in the morning and 25o C - 27o C in the afternoon. As previously reported, fish were observed for five minutes at each meal and adjustments in the size of the next meal was based on how well the fish fed during the five minute observation period. Tank maintenance consisted of siphoning 1/10 of the tank volume each morning approximately 30 minutes before being fed. In the afternoon, 1/4 of the tank volume was siphoned prior to receiving the afternoon meal. A near complete water change for each of the tanks was conducted on a weekly basis at which time all tanks were scrubbed clean. In all cases water was replaced with aerated tap water that was aged for a minimum of one day.

Growth was determined using the same tanks and stocking density as for the palatability experiment. Each flake-food tested was given to fish in replicate tanks. Tank maintenance and feeding procedures were the same as described above. The length of the growout trial was 28 days at which time the final body lengths and weights were determined for each of the surviving fish and the data summarized statistically. The entire experiment was repeated with a different set of fish. The feed conversion ratio (FCR) for each tank was determined by dividing the weight of the feed provided by the weight gained by the fish.

 

RESULTS AND DISCUSSION

The composition of the three flake feeds used during the current study is summarized in Table 1.

Table 1. Proximate analysis of various flake-feeds used in the current investigation.
 

Feed Type  

Crude Protein (%)

 

Crude Lipid (%)

 

Crude Fiber (%)

 

Ash
(%)

 

Tetramin
Tri-Flake
Black Gold

 

49
47
46
 

 

6.2
9.0
20.0
 

 

7
6
3
 

 

10
13
11
 

All of the feeds possess similar amounts of crude protein, fiber and ash. They mainly differ in their crude lipid content. Black Gold has two to three times the amount of crude lipid than that found in the other flake feeds tested. Palatability is essentially determined by letting the fish tell us how much they like a particular feed by accurately measuring how much they eat. Care must be taken so that they are fed to satiation and no more, thus, the five minute rule must be strictly enforced. Results of the palatability trials are summarized in Fig. 1.

 

Figure 1.Palatability of three commercial flake-feeds to the emperor tetra. Bars not having the same alphabet is significantly (P<0.05) different.

From the data it is clear that Tetramin Flake food is favored significantly over both Tri-Flake and Black Gold. Although the difference between Tri-Flake and Black Gold appears to be slight, the values are statistically significant which in lay terms means that Black Gold is the least preferred of all the flake feeds tested by the emperor tetras.

A summary of the growth trials is presented in Table 2.

Table 2. Summary of growth trial of emperor tetras using three different flake feeds. Values with different superscripts are significantly (P<0.05) different.
 

Feed Type  

Replicates

 

Final Body Weight (mg)

 

Final Body Length (mm)

 

Survival
(%)

 

FCR

 

Trial #1
Tetramin
Tri-Flake
Black Gold

 


2
2
2
 

 


358ab
369a
323b
 

 


31.0ab
32.0a
30.5b
 

 


96
96
96
 

 


1.52
1.27
1.41
 

 

Trial #2
Tetramin
Tri-Flake
Black Gold

 


2
2
2
 

 


504
499
509
 

 


35.0
35.5
36.0
 

 


100
100
100
 

 


2.28
2.06
2.52
 

 

In contrast to the clear differences observed in the palatability trials, the resulting growth for the emperor tetras obtained with the three different flake feeds does not correlate well with the palatability results. During the first growth trial Tetramin and Tri-Flake were tied for having the largest fish after the 28 day trial with Black Gold resulting on average with the smaller fishes. During the second trial no statistical difference could be detected in growth between all three flake feeds. The results at first may seem contradictory as one would logically expect if the fish like a particular feed more and eat more per feeding they would grow larger. This was the case that we previously reported with koi (I'a O Hawai'i, Vol. 1997, Issue 6) where the palatability of a number of koi feeds were tested and a good correlation in palatability and resulting growth of a particular feed was found. In that study the nutritional quality of the feeds appeared to be equal. However, this is not the case for the current investigation as the "new flakes" have higher crude lipid levels than does Tetramin and may be one reason for the similar rates of growth recorded during the experiments.

We start to see a familiar pattern with regard to the freshwater ornamental fish feeds that are developed for use by pet-owners. For Tetramin at least, it has a superior palatability than the two new flake feeds developed. This is important for the pet owner as one of the main pleasures of raising aquarium fish is to watch them feed with vigor when provided food. The superior palatability results for Tetramin have also been seen when tested with other species (results to be featured in future articles) and does not appear to be species specific. This is good news for the producers of Tetramin. It does, however, have one flaw and that it has a very low crude lipid content and from an aquaculturists point of view does not support maximal growth. We are therefore faced with a dilemma when answering the question, what is the best food for my fish? When asked this question do not be surprised to be answered with another question, "which is more important to you, fish enjoying their food or what makes the grow well?" The situation reminds us of our childhood experiences when being told by our parents to, "eat your vegetables because they're good for you". We all knew that it was good for us but it sure didn't taste good.

Palatability is essentially determined by letting the fish tell us how much they like a particular feed by accurately measuring how much they eat. Care must be taken so that they are fed to satiation and no more, thus, the five minute rule must be strictly enforced. Results of the palatability trials are summarized in Fig. 1. From the data it is clear that Tetramin Flake food is favored significantly over both Tri-Flake and Black Gold. Although the difference between Tri-Flake and Black Gold appears to be slight, the values are statistically significant which in lay terms means that Black Gold is the least preferred of all the flake feeds tested by the emperor tetras.