1. Introduction

The ornamental fish sector is a widespread and global component of international trade, fisheries, aquaculture and development. Ornamental fish keeping is becoming popular as an easy and stress relieving hobby. About 7.2 million houses in the USA and 3.2 million in the European Union have an aquarium and the number is increasing day by day throughout the world ^[1]. Comets are smaller than the common goldfish and only grow to a length of about 6 to 10 inches in an aquarium, but they can reach a length exceeding 12 inches in a large pond. Under optimum conditions, the tails can grow up to 12 inches in length and may live up to 7 to 14 years ^[2]. Comets goldfish are omnivorous and easy to feed and accept what is offered. They prefer most food sources including flake food and pellets ^[3]. Cyprinid larvae are known to prefer natural food items such as free living protozoa and rotifers, and larger planktonic organisms like cladocerans and copepods at fry and fingerling stage ^[4].

For propagation of a fish species knowledge of feeding habit is very essential as it plays a vital role in the growth pattern. Food is the main source energy and plays an important role in determining the population levels, rate of growth and condition of fishes ^[5]. The proper growth of fish depends on quantity and quality of food having all the essential nutrients ^[6]. Growth of an organism can be defined as a change in its size (length and weight) over a period of time. The growth rate in fishes is highly variable and depends upon many environmental factors. Quality of food and its availability is one of the important factor influences growth rate of fish ^[7]. The growth rate of larvae is also influenced by the quality of feed and their acceptability ^[8]. In aquaculture feed is the single most important item since nearly 60% cost is associated with fish feed ^[9].

The present study was conducted to find out the proper feed (protein level) for larval growth and survivability of comet goldfish (Carassius auratus) larvae in the congested fiber glass aquaria.

2. Materials and Methods

The experiment was conducted for 60-day long from 20th December, 2010 to 15th February, 2011 in fiber glass aquaria volume (30×11×8 inch³) in the fish physiology laboratory of Fisheries and Marine Resource Technology Discipline, Khulna University, Bangladesh. In this experiment there were three treatments and each treatment consisted of two replications supplied with three dissimilar feeds i.e. treatment T1 (crushed pellet feed), treatment T2 (mixed diet i.e. 50% pellet + 50% chopped tubificid worms) and treatment T3 (live chopped tubificid worms). Each of the experimental units of 45 larvae was stocked and their average length were 2.21 ± 0.03, 2.23 ± 0.04 and 2.25 ± 0.05 mm respectively in three treatments and their average weight was 0.005 ± 0.001 g respectively. PG dose was used for artificial propagation of the brood fish for production of larvae. Then the larvae were reared in the glass aquaria up to three days and nourished along with boiled eggs for avoiding biasness of outcome. Prior to storing of larvae, each of the fiber glass aquaria was prepared of dirt free up and equipped with all conveniences so that the experimentation runs sound powerfully. About 50% water from each aquarium was partially substituted through hygienic water at every alternate day before feeding. Appropriate aeration was done to supply adequate oxygen into the aquaria by motorized aerator it was nonstop till the conclusion of the research. The feces in each aquarium were removed by siphoning and the dead larvae were removed and reckoned in the morning and in the evening prior to feeding. Proximate composition of feeds were examined following the standard methods given by Association of Official Analytical Chemists ^[10] in the Fish Nutrition Laboratory of Fisheries and Marine Resource Technology Discipline, Khulna University, Khulna. The larvae stocked under the different treatments were fed with different feeds administered those three times daily at 7:00, 3:30 and 12:300 h. Sampling was made at every 7 days interval. Ten larvae were arbitrarily collected from each aquarium to obtain the length and weight data. The weight (g) was taken in an analytical balance and the length (mm) was measured by placing the fry on a transparent petridish placed on a 1 mm graph-paper. Sampling was done before the application of feed to avoid the biasness of weight due to presence of excessive feed. The following formulae were used to determine the different growth parameters

a) Length gain of larvae was calculated by ^[11].

b) Weight gain of the larvae was calculated by the following formula ^[11].

c) Specific growth Rate (%)

According to ^[12] the specific growth rate of prawn was calculated as, Specific growth rate

Where, W₂ = Final live body weight (g) at time T₂

W₁ = Initial live body weight (g) at time T₁

d) The survival rate was calculated by using the following formula ^[13]

e) Feed Conversion Ratio (FCR)

Feed conversion ratio was calculated by using the following formula ^[14].

Spread sheet analysis of data was done by using Microsoft Excel, version 5.0, Microsoft Inc. USA. To analyze the data analysis of variance (ANOVA) followed by Duncan’s Multiple Range Test (DMRT) ^[15] was done by using SPSS 16.0 for windows® ^[16]. Standard (± error) of treatments means were calculated from the residual mean square in the analysis of variance.

Table 1. Proximate composition of feeds used for rearing of C. auratus for 60 days (% dry weight)

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Table 2. Growth performance of comet gold fish, C. auratus larvae of different treatments after 60 days rearing, (mean ± SE)

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3. Result and Discussion

The 60-day long experiment was performed with a view to observing the effects of different feeds on growth and survival of comet gold fish larvae. Proximate composition of feeds were analyzed and given in Table 1. The initial average length of the larvae were 2.21 ± 0.03, 2.23 ± 0.04 and 2.25 ± 0.05 mm in all treatments respectively and the initial average weight of the larvae were 0.005 ± 0.001 g for all treatments. The final average length of the larvae of treatment T1 (crushing pellet feed), T2 (mixed diet i.e. 50% pellet feed + 50% chopped tubificid worms) and T3 (live chopped tubificid worms) were 22.11 ± 0.53 mm, 23.8 ± 0.48 and 25.9 ± 0.47 mm at the same time as the final average weight were 0.22 ± 0.009 g, 0.25 ± 0.010 g and 0.32 ± 0.027 g respectively (Table 2).

The highest length gain was found to be 10.4 ± 1.19 mm in treatment T3 (fed with chopped tubificid worms) which is significantly (P < 0.05) higher than the rest of two treatments (Figure 1). Likewise, the highest gain in weights of the larvae was 63 ± 0.025 g in treatment T3 (fed with live tubificid worms) which is significantly (P < 0.05) higher than those of the other two treatments (Figure 2) followed by 48.6 ± 0.037g in treatment T2 (fed with mixed diet) and 43.2 ± 0.126 g in treatment T1 (fed with crushed pellet feed).

Figure 1. Weekly variation of length increment among three treatments during 60 days experimental period. Vertical bars represented ± standard error

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Figure 2. Weekly variation of weight increment among three treatments during 60 days experimental period. Vertical bars represented ± standard error

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The highest percent length gain was 100.4 ± 6.03% and percent weight gain was 630 ± 33.73%, respectively as observed in the larvae fed with live tubificid worms (Table 2). After completion of the experiment, the highest specific growth rate was found to be 1.33 ± 0.02% shown by the larvae fed chopped tubificid worms (Table 2) which was significantly (P<0.05) higher compared to those in treatment T₁ and T₂ (Figure 3). The survival rates were found to be 64.44 ± 2.46%, 57.7 ± 3.01% and 51.11 ± 2.10%, respectively in T₃, T₂ and T₁ (Figure 4).

According to ^[17] depicted growth rate of fish increases within the level of dietary protein till the optimum level is reached. ^[18] Suggest that growth, reproductive potentials, and survival of each species are affected by the nutrient conditions of the culture media. In the present study the experiment was conducted in closed condition in the aquaria that were different than any natural environment. Cyprinid larvae are prefer to natural food items such as free living protozoa and rotifers, and larger planktonic organisms like cladocerans and copepods at fry and fingerling stage ^[4]. Live-food has been the most useful feed for rearing of fry of Coregonus lavaretus ^[19]. It also plays an important role in the shrimp and salmon industry. Among the different live-foods e.g. rotifers, Brachionus spp., Moina sp., Artemia sp. etc. tubificid worms are very popular and cheap live-food used for feeding larvae of carnivorous and omnivorous fish species ^[20]. Considerably better growth and survival rates of larvae and fry were observed with tubificid worms over formulated feeds in a number of catfish species such as ornamental koi carp, Cyprinus carpio ^[21], Channa striatus ^[22] Clarias batrachus ^[23]. The results of the present experiment also suggest the suitability of live chopped tubificid worms as the best food of C. auratus larvae.

Stocking density is known as one of the important parameters in fish culture, since it directly affects growth and survival, and hence production ^[24]. ^[25] Conducted an experiment with the larvae and juveniles of Clarias gariepinus and concluded that growth and survival was density dependant and that live food was preferred to formulated feed. In this experiment the stocking density was 45 larvae in each aquarium that was an acceptable density in respect of previous research works. However, the hatchlings fed with formulated feed showed very little interest according to ^[26]. The feeding frequency of 3 times/day was adopted during the present experiment to avoid water fouling and ease of feed provision and other managements. Feeding frequency has direct impact on the growth performance and survival of fry and larvae of Clarias macrocephalus ^[27]. They found that a feeding frequency of three times in each day was best for rearing the fry and larvae of Clarais macrocephalus which is relevant to the present study.

Figure 3. Comparison of specific growth rate (SGR%) of larvae fed with chopped pillet feed, mixed feed and live tubificid worms during 60 days experimental periods. (Vertical bars represented ± standard error. Columns marked with the different letters are significantly different)

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Figure 4. Comparison of survival rate of larvae fed with pellet feed, mixed feed and live tubificid worms during 60 days experimental periods. (Vertical bars represented ± Standard error. Columns marked with the different letters are significantly different)

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The available information suggests that the survival rate is very poor in earlier stage of the life cycle. In treatment T₁ the survival rate was lower than that of other two treatments because, pellet feed was used in treatment T₁ which deteriorated the water quality much than other two treatments. This result may be due to poor physiological development of earlier stage of life.

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