Fish fingerlings transport related stresses and mortality in Bangladesh | |
| Author | Hasan, Mahmud |
| Call Number | AIT Diss. no.AQ-07-09 |
| Subject(s) | Carp--Bangladesh Fishes--Breeding--Bangladesh |
| Note | A dissertation submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Aquaculture and Aquatic Resources Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AQ-07-09 |
| Abstract | Carp seed trading is a robust, and a growing sub-sector of Bangladesh aquaculture. It is estimated that over 100,000 people are engaged in carp seed trading and transport. They are one of the poorest, least educated and vulnerable, and least understood sub-population in Bangladesh. These traders have been playing a vital role in the expansion of aquaculture in the country. Unfortunately, no studies have been undertaken to understand their livelihoods and little is written about their vulnerabilities. This study, therefore, was designed to assess these issues. Additionally, this study intended to identify the current technical and research problems facing the carp seed traders. The livelihoods and vulnerability of the carp seed traders were assessed by structured household (HH) survey. The purposive sampling technique was used to collect the data using group discussions, semi-structured surveys, and structured HH surveys as the primary tools. The HH assets were found to be not sufficient enough to maintain the current living standards. Carp seed trading was found to be the main source of livelihoods for the traders (>50% HH income for 77% traders). The risk from carp seed mortality was found to be the major source of vulnerability. This study indicated that livelihoods of the carp seed traders could be improved by the increased and sustained income to the HH through improved fingerling survival during and after handling and transport. In order to improve the livelihoods of the carp seed traders, a series of experiments were conducted first, to understand the stressors and their levels. A second series of experiments were conducted to improve survival, health and growth by minimizing stress levels. Conditioning is the acclimation of fish prior to transport. Fingerlings are conditioned by repeated netting every morning for 3-4 sequential days by transferring them from nursery to conditioning pond. The effects of 1 h truck transport from nursery to carp seed market were evaluated using conditioned and unconditioned silver carp, Hypophthalmichthys molitrix fingerling at a loading density of 62.5, 125.0 and 187.5 g L⁻¹. Unconditioned silver carp fingerling had 5-folds higher mortality than did the conditioned ones. Plasma cortisol between the conditioned and unconditioned silver carp fingerling were similar while the chloride level (21.44 ± 1.83 meq L⁻¹) in the unconditioned fingerling was 3-times lower than in the conditioned ones (62.56 ± 0.93 meq L⁻¹). The effects of three levels of loading densities (e.g., 200, 300 and 400 g L⁻¹) and four levels of durations (1, 3, 6 and 9 h) on the mortality, plasma cortisol and chloride levels, bacterial abundance and growth in rohu, Labeo rohita fingerlings were evaluated in a transport simulation. While the total immediate mortality was low (4-12%), the delayed mortality was high (27-49%). Initial capture and handling was found to be the most stressful phase indicated by elevated plasma cortisol, although levels of cortisol continued to rise 6 and 9 h after transport. The highest level of cortisol was observed 9 h after transport. Level of plasma chloride dropped after transport across all density and treatment durations. Specific growth rate (SGR, % d⁻¹) and total bacterial density (cfu g⁻¹) were not different between and within treatments, and between treatments and control. The results of this experiment suggest that transport has a profound effect on the stress responses in rohu fingerling. Although the level of immediate mortality was low, the level of delayed mortality was significantly higher with production efficiency implications to grow-out farmers. The effects of fingerlings immersion in low-dose benzocaine (15 mg L⁻¹ for silver carp & 30 mg L⁻¹ for rohu) and quinaldine (100 uL L⁻¹ for silver crap and 250 uL L⁻¹ for rohu) for 1, 3 and 6 h on the stress responses and survival of rohu and silver carp fingerlings was evaluated in a transport simulation. Both anesthetics treatments had significantly (p<0.05) lower mortality (0-2%) than the control. The total mortality in the control (without anesthesia) was 30% in rohu and 14% in silver carp. Quinaldine and benzocaine treated fingerlings had significantly higher plasma chloride levels than the control in both species. Benzocaine, quinaldine as well as control had initial elevated cortisol levels. Benzocaine lost effectiveness 3 h after exposure while quinaldine persisted throughout the 6 h period. Both sedatives had lower bacterial build up (quinaldine: 3.12 ± 0.20x 10² and 2.62 ± 0.26x10² cfu g⁻¹; benzocaine: 4.22 ± 0.26x10² and 2.16 ± 0.07x10² cfu g⁻¹) compared to the control (rohu: 5.67 ± 0.27x10⁴ cfu g⁻¹; silver carp: 4.53 ± 0.24x10² cfu g⁻¹). No post exposure mortality was observed in any of the transport methods assessed 48 h after treatment. This study first indicated that carp seed traders are vulnerable to the variable mortality of fish fingerlings. Even a small increment in the survival could significantly increase income and reduce vulnerability. Subsequent experiments showed that conditioning prior to transport, loading density and durations affect fingerling survival. Although loading density and transport alter plasma cortisol and chloride levels resulting in high level of immediate and delayed mortality, holding durations or density did not reduce the growth rates. Well conditioned rohu fingerling up to 9 h at 300 g L⁻¹ is likely to result in little immediate mortality. Low dose quinaldine could significantly reduce mortality during transport in the long distance (6 h of transport) and high density (400 g L⁻¹) conditions in rohu and silver carp fingerlings while benzocaine is more appropriate for shorter hauls (3 h) |
| Year | 2007 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AQ-07-09 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Bart, Amrit N.; |
| Examination Committee(s) | Gallardo, Wenresti G.;Rakshit, Sudip Kumar; |
| Scholarship Donor(s) | University Fisheries Education & Research, DFID/UK; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2007 |