The spawning pattern, length-weight relationship and condition factor of elephant fish, Mormyrus rume from the Bontanga reservoir, Ghana

 

Author(s): Alhassan EH, Abobi SM, Mensah S, Boti F

Abstract: A study was conducted into the Spawning pattern, Length-Weight Relationships and Condition factor of Mormyrus rume in a shallow reservoir in the Northern Region of Ghana. One hundred and sixty seven   specimens were used during the study period. Males were 92 (55.1%) and females were 75 (44.9%) respectively. The reproductive pattern was studied within a specified period of five months (December 2010 to April 2011) by determining the sex ratio, gonadosomatic index (GSI), condition factor (K) and assessing the gonadal development of Mormyrus rume. Immature and maturing gonads were predominant in March and April respectively and gonads ripped in January and February. The patterns of gonad development in female the Mormyrus rume indicated that spawning was not synchronized. The gonadosomatic index (GSI) ranged from 1.29- 3.56 indicating that species were in good condition to grow and reproduce. Measurement of total length and standard length of each individual fish was taken to the nearest 0.10 cm. Total body weight of each individual fish was determined to the nearest 0.10 g. Counts of sexes were also determined for the sampled fish collected fortnightly by purposive sampling of the species from the fishermen’s landing sites on the reservoir. It was revealed that Mormyrus rume has the allometric growth with b = 2.880 ± 3.092 and a = 0.031 ± 0.021 (n = 167). The condition factor (K) for the specimensranged between 1.422 and 2.90 for females and 1.49 and 2.21 for the males. Males predominated over females with a sex ratio of 1.2:0.8 (male: female) and a chi-test (x2) of 9.49 at P<0.05. Also, the relationship between the weight and the length was W=0.0310L2.986 with coefficient of determination r2 = 0.8120 respectively. There was no clear pattern in both growth parameters for the study period, indicating that there was no significant influence of high and low water levels on the growth performance of the fish. The best fish condition was recorded for those specimens with length of between 12.1 and 18.2 cm (SL) and 13.3 and 19.4 cm (TL) that was coincided with the maturation stage of the fish.

Fig: The monthly total lengths (cm) and total weights (g) relationship of males Mormyrus rume in the Reservoir at Bontanga.

Fig: The monthly total lengths (cm) and total weights (g) relationship of females Mormyrus rume in the Reservoir at Bontanga

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