Abstract
The effects of in-feed probiotics on growth performance, haematological parameters, gut microbial content, and morphological changes to pangasius fish were assessed. The trial had three phases, i.e., larvae to fry (20 days), fry to fingerlings (45 days), and grow-out phase from fingerlings to marketing (90 days). The stocking densities were 400 m-3, 200 m-3, and 12 m-3 for phases 1, 2, and 3, respectively. Phases 1 and 2 were conducted in hapas in the same pond, whereas phase 3 was performed in concrete tanks. The in-feed probiotic was administered at a rate of 0.2 g kg-1 of feed three times per day in phases 1 and 2 only. In phase 3, in-feed probiotics was not applied to any groups. The treated group exhibited higher growth performances (p < 0.05) than the control in all three phases of experiment. The survival % in phase 1 and 2 were found significantly (p < 0.05) higher in treatment groups. This indicates that pangasius nurserers would benefit from using probiotics as a safeguard to increase fry survival to a greater extent. Two haematological parameters including red blood cells (RBC) and white blood cells (WBC) levels were found significantly (p < 0.05) higher in treated groups in phase 2 and 3, while glucose and hemoglobin level were found significantly (p < 0.05) higher in the treated groups during phases 2 and 3, respectively. The gut microbiota content was relatively higher in the treated groups in phase 2 and 3. Histological findings indicate that the use of probiotics during the nursing phases of pangasius induced a positive change in the intestinal morphological structures. The positive impacts of probiotics on the phase 3 confirmed an immediate and long-term growth performance and health of pangasius.
Highlights
Bangladesh is the 5th largest aquaculture producing country that produced more than four million metric tons (MT) in 2016–2017 (DoF, 2017; FAO, 2018), and total pangasius production reached 441, 643 MT in 2017–2018, which represented 23.24 % of aquatic produc tion (DoF, 2018)
Phase 1 The final weight, weight gain, average daily growth, and Specific growth rate (SGR) were non-significantly higher in the treatment group than those in the control group (Table 1)
In most cases, all pa rameters related to growth performance, except condition factor and SGR, were found relatively higher in the TT group followed by TC, CT, and CC
Summary
Bangladesh is the 5th largest aquaculture producing country that produced more than four million metric tons (MT) in 2016–2017 (DoF, 2017; FAO, 2018), and total pangasius (catfish) production reached 441, 643 MT in 2017–2018, which represented 23.24 % of aquatic produc tion (DoF, 2018). The late cycle fry may be kept for a longer period to produce over wintering fingerlings for the early stocking of grow-out ponds in the subsequent year. Phase 1– Larvae to fry: farmers usually stock about 2 kg of larvae per 0.13 ha pond maintaining a stocking density of 15 m− 2 where larvae are intensively fed for 10–12 days. It usually takes four weeks for the larvae to grow into fry (0.3–1.0 g). A high fry stocking density at this stage often results in mass mortality This phase may take from 45 to 60 days to produce fingerlings (14–20 g). Phase 3 – Fingerlings to adult (marketable size fish): the fingerlings are stocked for 7–8 months to achieve a marketable size (approximately one kg per fish)
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