One of the pathways for the entry of bacteria, both pathogenic and probiotic, into the larvae of fish hatcheries is via live prey.
As an inoculative mean for probiotic to digestive tract of larvae, live prey may be cultured and bioencapsulating with probiotics (Planas et al., 2004). Bacteria colonies the intestines of the larvae enter from the mouth opening (Hansen and Olafsen, 1999).
The initial establishment of a micro flora in the larval stages depends, among other factors, on the micro biota associated with eggs and newly hatched larvae, micro algae, and live prey introduced into the system and water of the rearing system (Keskin et al., 1994).
Live preys are important carriers of bacteria to the larval digestive tract (Blanch et al., 1997). Probiotics, live microbes that may serve as dietary supplements to improve the intestinal microbial balance, have received some attention in aquaculture (Irianto and Austin, 2002).
Artemia urmiana predominantly one of the most live foods that using in larviculture of sturgeon fish. The present study was conducted to determine the effects of graded levels of the probiotic bacillus, in bioencapsulation of Artemia urmiana on the growth parameters and feeding efficiency of Acipenser nudiventris larvae. This study was done in center of Marjanii sturgeon culture of Iran, for 2 weeks.
Materials and methods
The probiotic bacilli were prepared from Protexin Co. (Iran- Nikotak). The five species of probiotic bacillus (Bacillus licheniformis, B. subtilis, B. polymixa, B. laterosporus and B. circulans) as bacterial blend under the commercial title of Protexin aquatic were used for bioencapsulation of Artemia urmiana.
Three concentrations of bacterial suspension, 1×108, 2×108 and 3×108 bacteria per milliliter (CFU/lit) were provided. The Artemia urmiana were bioencapsulated in three doses of bacterial suspensions for 10 h. at 29±1oC, in glass con with 1 liter of seawater (3.0% salinity) at a density of 2.0 g / liter with constant illumination and oxygenated through by setting air pump (Gomez-Gil et al, 1998).
The bioencapsulated nauplii were used as a vector to carry probiotic bacillus to digestive system of Acipenser nudiventris larvae. Twelve fiberglass tanks (capacity of 50 liters) with three replicates for treatment and control were used.
Healthy larvae of Acipenser nudiventris provided by the fish hatchery of sturgeon center of Marjanii (Iran). The density of fish larvae in per tank was 4-5 fish per litre. Initial weight of fish larvae was 27 mg and length 16 mm.
Sturgeon larvae were fed based on the 30% of their body weight for six times a day with bioencapsulated Artemia nauplii in experimental treatments and unbioencapsulated Artemia nauplii in control treatment respectively. In the termination of experiment, fifty larvae from each tank were sampled and total weight and length of body were measured.
The growth and feeding parameters of Acipenser nudiventris at the end of the feeding trial and mean values of feeding parameters were shown in table 1.
The results indicated that the probiotic bacillus significantly promoted final body weight, body length and specific growth rate (SGR %) in experimental treatments in comparison with control treatment (p less than 0.05). While the condition factor (CF) weren't significantly increased (p more than 0.05).
The maximum body weight obtained in treatment of T3 (212.88 mg) while this parameter in control treatment was 179.33 mg. In experimental treatments the probiotic bacilli had positive and significant effects on the feed conversion efficiency (FCE %), Protein Efficiency Ratio (PER), Lipid efficiency ratio (LER) and energy efficiency ratio (EER) (p less than0.05). The best PER and LER obtained in T3.
The FCR showed an inverse correlation with concentration of bacillus (CFU/ liter) of bioencapsulated suspension of broth and the minimum of this parameter was obtained in treatment of T4 (3.38). The relative food intake (RFI %) in experimental treatments (T1, T2 and T3) had significantly decreased in comparison with control treatment (p less than 0.05). The maximum of RFI% obtained in control treatment (28.53%).
Discussion and conclusion
This study highlights the effects of probiotic bacilli on the enhancement of feeding efficiency and growth parameters of Acipenser nudiventris larvae.
Artemia urmiana is one of the most important live foods that were used as a vector to carry probiotics to digestive system of Acipenser nudiventris larvae. The best SGR and the highest body weight were obtained in T3. All the probiotic treatments resulted in feeding efficiency better than that of control treatment.
Similar effects had been reported for other fishes to increase considerably with the use of probiotic bacilli by Gatesoupe (1991) in using B. toyoi on turbot (Scophthalmus maximus) and Swain et al. (1996) in Indian carps that improved the growth factors and feeding efficiency of carp.
However, in trial T3, the sturgeon larvae were fed by bioencapsulated Artemia urmiana in suspension of 3×108 bacteria per milliliter, obtained the best body weight and SGR, which showed both of them could promote each other.
Also Bacillus subtilis and B. circulans supplemented in diets of rohu (Labeo rohita) fingerlings showed that the final body weight and SGR significantly increased (Bairagi et al., 2004).
Results of this study also showed that different concentration of probiotics could cause different effects on growth parameters and feeding efficiency. The present experiment indicated that the probiotic bacillus highly increase the growth performances and feeding efficiency in Acipenser nudiventris larvae.
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