| Author | Ahmad, Sultanul Arifin Shameem |
| Note | A dissertation submitted in partial fulfillment of the requirements for the
degree of Doctor of Technical Science in
Aquaculture and Aquatic Resources Management, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | This study consists of three experiments to assess the impact of introduced Nile tilapia
(Oreochromis niloticus) on the small indigenous fish species (SIS) of Bangladesh and
Nepal. These studies assess the effect of mixed-sex and mono-sex male tilapia on changes
in population structure, recruitment and dietary overlap of SIS in different region and
environment. The purpose of these studies was to determine the degree of dietary overlap,
the population structure of experimental SIS, recruitment number, biomass, and preference
level of feed and dietary overlap among the species in each of the treatments.
The first study was conducted in Bangladesh Agricultural University (BAU), Mymensingh,
Bangladesh. Small earthen ponds of 100 m2 were stocked with mixed sex or all male Nile
tilapia (Oreochromis niloticus) with or without SIS commonly found in south Asia, mola
(Amblypharyngodon mola) chela (Chela cachius) and punti (Puntius sophore). Ponds were
fertilized and then stocked with 0.56 m–2 in the mixed-sex and mono-sex all male tilapia
treatments and 0.42 m–2 in the treatment without tilapia. No additional nutritional inputs
were applied after stocking. There were three different treatments, mixed-sex tilapia with
SIS (T1), mono-sex male tilapia with SIS (T2) and only SIS without tilapia ((T3-Control).
All treatments were stocked with equal number (14) of each fish. All species reproduced
during the 21-month culture duration. The number of recruits varied by species, although
tilapia reproduced in greater number than SIS. Tilapia numbers at harvest were the highest
(451±25/100 m2) in the mixed-sex treatment compared with mola (221±22/100 m2), chela
(94±8/100 m2) and punti (100±7/100 m2). The number of mola was highest (399±33/100
m2) in the mono-sex all male tilapia treatment. There were lower number of mola and chela
in the treatment containing mixed-sex tilapia. Gut content analysis combined with water
sampling revealed that all fish species fed selectively. Greater significant interspecies
dietary overlap was found between Nile tilapia and SIS (0.70 to 0.79) and among SIS (0.65
to 0.70) in the mixed-sex tilapia than mono-sex male tilapia treatments (0.64 to 0.66
between SIS and Tilapia, 0.55 to 0.58 among SIS). These results showed that there is
potential for tilapia to compete with local indigenous fish species when space and other
resources are limiting.
Another study was conducted to assess the effects of mixed sex and mono-sex all male
Nile tilapia (Oreochromis niloticus) on punti (Puntius sophore), darai (Esomus danricus)
and faketa (Barilius barna) in the Institute of Agriculture and Animal Science (IAAS),
Rampur, Chitwan, Nepal. Experimental design and the methodology was similar as
Experiment I except for the two species. All species had reproduced during the 14-month
culture duration. The number of recruits varied by species, although tilapia reproduced in
greater number than SIS. Tilapia numbers at harvest were the highest (1046±744/100 m2)
in the mixed-sex treatment compared to punti (54±23/100 m2) and darai (46±33/100 m2).
The number of darai (512±473/100 m2) and punti (1070±248/100 m2) was highest in
without tilapia treatment and significantly different from mixed-sex tilapia treatments and
mono-sex male tilapia treatment. Number of darai and punti in mono-sex male tilapia
treatment also significantly higher than mixed-sex tilapia treatment. Among the SIS, faketa
only the SIS did not spawn in any treatments due to the absence of suitable spawning and
breeding environment. There were fewer of punti and darai in the mixed-sex tilapia
treatments compared with the other treatments. All fish species fed selectively. Only
significant interspecies dietary overlap was found between Nile tilapia and SIS (0.65 to
0.71) in mixed sex tilapia treatments.
iv
The final study was conducted upon completion of first two studies to assess the effects of
mixed-sex Nile tilapia (Oreochromis niloticus) on three SIS, mola, chela and punti in
simulated open water body (1000 m2). There were two treatments without replication.
Treatments were: mixed-sex tilapia with SIS (T1) and only SIS without tilapia ((T2-
Control). Ponds were fertilized and then stocked with 1 fish m–2 in the mixed-sex tilapia
treatments and 0.75 m–2 in the without tilapia treatment. No additional nutritional inputs
were applied after stocking. All treatments were stocked with equal number (250) of each
species. All species reproduced during the 14-month culture duration. The number of
recruits varied by species, although SIS recruitment was greater number than tilapia.
Tilapia numbers at harvest was lower (2585/1000 m2) in the mixed-sex tilapia treatment
compared to mola (4285/1000 m2) and similar to the punti (2563/1000 m2) and chela
(2558/1000 m2). The number of mola was highest (4830/1000 m2) in the without tilapia
treatment followed by punti (3543/1000 m2) and chela (3233/1000 m2). There were lower
number of mola, chela and punti in the treatment containing mixed-sex tilapia. Gut content
analysis combined with water sampling revealed that all fish species fed selectively similar
to other two experiments. Biologically significant interspecies dietary overlap was found
between Nile tilapia and SIS (0.61 to 0.66). Among the three studies, higher recruitments
rate of SIS and lower degree of dietary overlap between tilapia-SIS and among SIS were
observed in simulated open water bodies than the simulated small ponds.
The study demonstrated a relatively low negative effect of Nile tilapia on indigenous small
fish species because no indigenous species was lost (except faketa) from treatments ponds
and a healthy population of SIS was found to reproduce in the experimental ponds.
However, lowest recruitment of SIS in the mixed-sex tilapia treatment, the selective
feeding nature of tilapia and SIS food habits combined with significant interspecies dietary
overlap suggests the potential for competition. Therefore, longer duration study with
varying level of management is needed to determine how successfully tilapia competes
with locally adapted SIS. |
| Year | 2010 |
| 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 | Agricultural and Aquatic Systems (AS) |
| Chairperson(s) | Bart, Amrit N. ; |
| Examination Committee(s) | Athapol Noomhorm ;Gallardo, Wenresti G. ;Wahab, Md. Abdul ; |
| Scholarship Donor(s) | Pond Dynamics/Aquaculture Collaborative
Research Support Program (CRSP), USAID; |