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Analysis of growth and mortality from daily growth increments in the otoliths of dagaa (Rastrineobola argentea) in Nyanza Gulf, Lake Victoria, Kenya Njiru, Murithi
Abstract
Prior to 1960, Rastrineobola argentea was of little economic importance in terms of catches in Lake Victoria. Catches have increased in the last 15-20 years and it is now become the second most important commercially targeted fish species. Growth and mortality parameters of R. argentea, a tropical cyprinid, were estimated using growth increments in otoliths and length-frequency analysis to gather more biological data on the species. The Gompertz growth curve yielded the best fit for the juvenile population. Growth and population parameters for the commercial catch show a growth rate coefficient (K) of 1.8 yr⁻¹ with L∞ of 5.0 cm standard length (SL) in Nyanza Gulf and K of 1.5 yr⁻¹ with L∞ of 6.5 cm SL in the open waters site. Instantaneous growth rates decreased with age, with fish from open waters showing a more gradual decline. The weight (g)-length (mm) relationship is W = 5.562L³⁻³. Fish immersed in 600 mg/L of tetracycline hydrochloride showed its incorporation within 12 hours and increments were likely formed daily. Juvenile fish mortality ranged from 11.3 to 29.9 yr⁻¹. Total mortality (Z) for adults estimated from length-converted catch curves was 4.0 and 4.8 yr"1 for Nyanza Gulf and the open waters respectively. Fishing mortality (F) estimated from catch and biomass was 0.98 yr⁻¹ for Nyanza Gulf, while that of open waters from length-converted catch curve was 1.4 yr⁻¹. The exploitation rate is 0.25 and 0.29 for Nyanza Gulf and open waters respectively. Two annual breeding peaks were observed in both Nyanza Gulf (May/ October) and open waters (May/November). Length and age at recruitment for L50% for Nyanza Gulf was 11.6 mm and 34.5 mm in open waters, corresponding to age of 44 and 175 days respectively. In comparison with published data on the growth and mortality of some small pelagics of African waters, R. argentea had low values of L∞, K, M and Z.
Item Metadata
Title |
Analysis of growth and mortality from daily growth increments in the otoliths of dagaa (Rastrineobola argentea) in Nyanza Gulf, Lake Victoria, Kenya
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1995
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Description |
Prior to 1960, Rastrineobola argentea was of little economic importance in terms of
catches in Lake Victoria. Catches have increased in the last 15-20 years and it is now
become the second most important commercially targeted fish species. Growth and
mortality parameters of R. argentea, a tropical cyprinid, were estimated using growth
increments in otoliths and length-frequency analysis to gather more biological data on the
species.
The Gompertz growth curve yielded the best fit for the juvenile population. Growth and
population parameters for the commercial catch show a growth rate coefficient (K) of 1.8
yr⁻¹ with L∞ of 5.0 cm standard length (SL) in Nyanza Gulf and K of 1.5 yr⁻¹ with
L∞ of
6.5 cm SL in the open waters site. Instantaneous growth rates decreased with age, with
fish from open waters showing a more gradual decline. The weight (g)-length (mm)
relationship is W = 5.562L³⁻³. Fish immersed in 600 mg/L of tetracycline hydrochloride
showed its incorporation within 12 hours and increments were likely formed daily.
Juvenile fish mortality ranged from 11.3 to 29.9 yr⁻¹. Total mortality (Z) for adults
estimated from length-converted catch curves was 4.0 and 4.8 yr"1 for Nyanza Gulf and
the open waters respectively. Fishing mortality (F) estimated from catch and biomass was
0.98 yr⁻¹ for Nyanza Gulf, while that of open waters from length-converted catch curve
was 1.4 yr⁻¹. The exploitation rate is 0.25 and 0.29 for Nyanza Gulf and open waters
respectively. Two annual breeding peaks were observed in both Nyanza Gulf (May/
October) and open waters (May/November). Length and age at recruitment for L50% for
Nyanza Gulf was 11.6 mm and 34.5 mm in open waters, corresponding to age of 44 and
175 days respectively. In comparison with published data on the growth and mortality of
some small pelagics of African waters, R. argentea had low values of L∞, K, M and Z.
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Extent |
5120463 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-01-20
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0074806
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1995-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.