The cichlid Sarotherodon galilaeus [1] is native to fresh and brackish waters in Africa [2]. In Sudan it was reported from the Nile and its tributaries [3-6]. It was also recorded from man-made Lakes. This included the lists from Lake Roseris [7,8]; from Jebel Aulia Dam Lake [9,6]; from Lake Nubia [10,11] and from Khashm El Girba Lake [12].

Sarotherodon galilaeus categorized as least concern [13], is an important captive fish and had been introduced for aquaculture purpose in several countries. Probably the first introduction was from Sudan to Congo in 1953 [14], from Israel to South Africa in 1959 [15]; from USA to Japan in 1964 [16] and from Africa to China in 1981.[15]

Studies on aspects of biometry of Sarotherodon spp., was of concern to West African ichthyologist working in different water bodies especially in Nigeria. Studies on S. galilaeus were due to [17-23,1] In Sarotherodon melanotheron these aspects were studied by Ayoade and[24-26,19,] 

The objective of this work is to compare the biometric of S. galilaeus from Nile and its tributaries in order to detect traits of significance in breeding studies.

Fish collection

Highly fresh S. galilaeus were collected from landing sites at Kosti (13°N, 32°E), Sinnar (13°N, 33°E) and  Al Sabaloga (18°N, 32°E). Fish identification followed [3]

Meristic counts

Eight meristic traits were counted. Number of dorsal fin spines (DFS). Number of dorsal fin rays (DFR). Number of anal fin rays (AFR). Number of pectoral fin rays (PeFR). Number of scales on upper lateral line plus those on the lower lateral line (LLS). The ratio between the number of scale starting from the dorsal fin origin towards the upper line and the number of scales starting from the anal fin origin, counting forwards and dorsally towards the upper lateral line (TRAS). Number of scales on pelvic fin (PVS). Cheek scale (CS).

Morphometric measurements

Measurements were taken with a dial caliper to the nearest 0.1 mm from the left side. Definitions and terminology of the traits given below followed.

Total length (TL). Standard length (SL). Body depth (BD). Head length (HL). Head width (HW). Inter orbital width (IOW). Snout length (SL). Lower jaw length (LJL). Premaxillary pedical length (PPL). Cheek depth (CHD). Eye diameter (ED). Lachrymal depth (LAD). Dorsal fin base (DFB). Predorsal distance (PRD). Anal fine base length (AFB). Pre-anal distance (PRA). Pre-pectoral distance (PRP). Prepelvic distance (PRV).  Caudal peduncle length (CPL). Caudal peduncle Depth (CPD). All these were recorded to 0.1mm and body weight (BW) to the nearest 0.1g.

Statistical analysis 

Data was subject to descriptive statistics and t-test. To decide which meristic trait contributed significantly in Canonical Discriminant Function (CDF), the Wilks' lambda (Λ) test was used. To determine rate of divergence among sites the Leave-one-out crosses validation was used. To develop correlation matrices, morphometric data was subject to simple regression analysis. Data analysis was perfumed by SPSS and Excel.

RESULTS

The mode of DFS, AFR and PeFR was similar in the three sites. The slight variability in the mean was related to differences in the count (Table 1). 

Table 1. Mean, mode and range of meristic counts of Sarotherodon galilaeus from the different study sites

Discriminant analysis showed clear overlap between S. galilaeus samples from Kosti and Sinnar and distinct separation of Al Sabloga samples (Fig. 1 and Table 2).

Table 2. Canonical Discriminant functions differentiating Sarotherodon galilaeus collected from the three study sites.

Fig. 1. Scatter plot of Canonical discriminant of Sarotherodon galilaeus from the three study sites.

Canonical Discrimination Function 1 separated Al Sabaloga sample from Kosti and Sinnar. This separation is extremely highly significant (p<0.000) as indicated by Wilks lambda (Table 3). Function 2 insignificantly (p>0.05) separated Sinnar sample from Kosti and Al Sabaloga (Table 3).

Table 3. The CDF and SCDF from discriminate analysis of Sarotherodon galilaeus from the three study site.

The reclassification of meristic counts, based on Leave-one-out cross validation, classified 75.0%, 92.3% and 100% of Kosti, Sinnar and Al Sabaloga samples respectively with an overall average at 100% (Table 4). The original grouped cases were 100% correctly classified. On the other hand, cross-validated grouped cases were correctly classified at an average of 89.10%. 

Table 4. Leave-one-out cross validation for Sarotherodon galilaeus collected from the three study sites.

Comparison between the mean value of 21 traits (Table 5), showed that: in Kosti samples the means of: BW and BD were very highly significant (p<0.001), TL. SL and PRA were highly significant (p<0.01), and DPF and PRD were significantly (p<0.05) higher compared with corresponding readings from Sinnar samples.

The growth mode in both sites was allometric positive as b-value >3.0. 

Table 5. Morphometric traits of Sarotherodon galilaeus from Kosti and Sinnar.

 ‘b’ is more than 3 (Fig. 2). 

             Regression analysis showed a linear relationship indicating significant correlation (p<0.05) between BW: TL; SL: TL and BD: TL, Figs. 2-4, respectively. The TL and BW regression showed a positive allometric growth because the regression coefficient

Fig. 2 Total length and body weight relationship in Sarotherodon galilaeus.

Fig. 3. Total length and standard length relationship in Sarotherodon galilaeus

Fig. 4. Total length and body depth relationship in Sarotherodon galilaeus

Sarotherodon galilaeus from Kosti showed a very high correlation between TL and SL (r-0.960) and a very weak correlation between PRV and IOW (r = -1.4E^-16). Cases of single Signiant correlation was found between SNL vs CPD (r = -0.600), and between ED and LAD (r – 0.650). 

In Sinnar samples a very high correlation was between BW: TL and BW: SL (r - 0.840) and a very weak correlation was between PRV and IOW (r = 9.18E^-05). 

Comparison between the correlation matrices showed that BW vs BD; TL vs BD and SL vs BD were very highly significantly correlated (p<0.001, Table 7) in Sinnar samples compared with the significantly (p<0.05, Tale 6) corresponding readings from Kosti samples.  In Kosti samples each of DFB, AFB, PRA was insignificantly correlated (p>0.05) with BD. In Sinnar samples insignificant correlation (p>0.05) was between AFB and BD.

Table 6. Correlation matrix in Sarotherodon galilaeus from Kosti*

*=Values < 0.423 are insignificant (p>0.05); readings from 0.423 to 0.536 are significant; from 0.537 to 0.652 are highly significant; readings ≥ 0.652 are very highly significant

.

Table 7. Correlation matrix in Sarotherodon galilaeus from Sinnar*.

*=Values < 0.288 are insignificant (p>0.05); readings from 0.288 to 0.371 are significant; from 0.372 to 0.464 are highly significant; readings ≥ 0.465 are very highly significant. 

DISCUSSION

Clear overlap between S. galilaeus samples from Kosti and Sinnar and distinct separation of Al Sabaloga samples was detected by Discriminant analysis. This is due to differences in habitats being typical riverine in Kosti and Sinnar and cataract in Al Sabaloga. Wilks Lambda test determined the level of significance of separation or overlap. While Leave-one-out cross validation correctly reclassified the grouping of specimens in the locations. The mode of DFS, AFR and PeFR was similar in the three studied sites. The slight variability in the mean was related to differences in the count of the traits between locations. [1] studied S. galilaeus from Ogun Coastal Estuary, Nigeria. They reported higher mean values in most of the meristic counts of female than the male populations, with significant difference (p<0.05) in pectoral fin rays. According to [24] in Sarotherodon melanotheron the fin rays were fairly constant unlike scales on the upper and lower lateral lines.

In the present study the TL of S. galilaeus ranged from 16.50 to 19.50cm; 12.8 to 20.0cm and 14-16.5cm in Kosti, Sinnar and Al Sabaloga, respectively. While the BW weight varied between 110 and 142g; 51 and140g and 40-51g; in Kosti, Sinnar and Al Sabaloga, respectively. [17] recorded a TL of (22-33cm) and BW of (250.0-814.0g). According to [20] TL of S. galilaeus ranged from 21 to 22cm while BW varied between 219 and 231g. This is related to differences in the productivity of their water bodies. 

Comparison between the mean value of 21 traits showed that in Kosti samples the means of BW, BD, TL, SL, PRA, DPF and PRD were significantly (p<0.05) higher compared with corresponding readings from Sinnar samples. The rest of the traits showed no significant differences between the two locations. [1] found higher mean values in most of the morphometric measurements of the female population than the males, but significant differences (p<0.05) were recorded in TL, SL and HL in S. galilaeus from Ogun Coastal Estuary, [17] found that S. melanotheron from Awba reservoir and Lagos lagoon, Nigeria showed significant differences (p<0.05) in BD and CPD, while SL, HL, HD, SNl, ED and CPL showed no significant differences (p>0.05). 

From Kosti and Sinnar S. galilaeus showed significant correlation (p<0.05) between BW: TL; SL: TL and BD. The correlation matrices of S. galilaeus from Kosti showed a very high correlation between TL and SL (r=0.960) and a very weak correlation between PRF and IOW (r = -1.4E^-16). Sinnar samples showed a very high correlation between BW: TL and between BW: SL (r= 0.840) and a very weak correlation between PRF and IOW (r = 9.18E^-05). 

The regression between TL vs BW showed a positive allometric growth as b>3.0 in Kosti and Sinnar populations. The regression analysis made by [19] (TL=0.025 +3.094BW) indicated isometric growth (b=3.094 which is ≈3.0). [17] derived TL=0.014+2.755BW for S. galilaeus. Its exponent ‘2.755’ showed negative allometric growth pattern. Negative allometric growth was recorded by [20] for female (BW=0.173 SL2.673) and for male (BW = 0.647 TL2.702); by[21] for males (LogW=0.725+1.230logL) and females (Log W=0.803+1.20 log L) in Oba reservoir, Nigeria; and by [23] 'b=2.91' from Ogling reservoir in Ghana. [18] found negative allometric growth for male (LogW= 1.125+2.846LogL) and female (LogW= 1.194+2.826LogL). The studies carried out in S. melanotheron recorded regression coefficient values of 2.80, 2.47 and 2.808 by [22,26] and[25], respectively, indicated negative allometric growth. worked in S. galilaeus over two years and found positive allometric growth, 3.12 for 2006 and 3.09 for 2007.

The body depth seems to be a treat to be followed in improvement of growth programmes. There is a need to unify the meristic counts and morphometric measurements to be studied as well as the statistical analysis to yield comparable results.   

Acknowledgements

Thanks are due to the Ministry of Higher Education and Scientific Research for funding this work. We are grateful to the Fisheries Research Center at Kosti and the Malaria Directorate at Sinnar for accommodation and laboratory facilities. 

The authors declare that they have no conflict of interest

No funding sources

The study was approved by the University of Khartoum,

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