Effect of elevated fry rearing temperature on survival rate, growth performance, and sex ratio of three Oreochromis niloticus populations of Ethiopian Rift Valley Lakes

Sex-reversal in Oreochromis niloticus is used to produce mono-sex males which are desired in aquaculture for better growth performances and population control. The present study was aimed at studying the effect of elevated fry rearing temperature on survival, sex ratios, and growth performances of O. niloticus populations of Lakes Chamo, Koka, and Ziway. Fries from five separate brood pairs of each population were either treated (T) in elevated fry rearing temperature of 36 ± 1°C or kept at room temperature of 24 ± 1°C as control (C) groups for 10 days (phase-I) and then grown in outdoor ponds for six months (phase-II). Survival rates in T groups (74.0 to 91.7%) were lower than that of C groups (83.3 to 97.0%) in all the three populations in phase-I but not in phase-II. Chamo population was better in survival rate (88.4% and 95.4% in Phase-I, and 95.4% and 95.3% in phase-II) than Koka population (85.8% and 91.3% in Phase-I, and 93.9% and 93.5% in phase-II) and Ziway population (80.2% and 88.6% in Phase-I and 90.2% and 91.9% in phase-II) both in T and C groups respectively. The Chamo population also attained significantly (p<0.05) higher mean final weight of 31.58 ± 6.78 g and 24.26 ± 6.67 g in T and C groups respectively, followed by that of Koka population with 21.70 ± 5.10 g and 18.83 ± 4.16 g while Ziway population with mean final weight of 17.49 ± 4.60 g and 16.81 ± 4.15 g was the least both in T and C groups. The overall sex ratios in T groups were skewed towards male but balanced in all C groups of each population.  Better growth was achieved only in T groups with higher male ratio than their corresponding C groups. The number of sensitive brooding pairs and the overall male ratio in T groups were higher in the Koka population (40%, 61.68%) than in Ziway (20%, 56.78%) and Chamo (20%, 56.39%) populations respectively. However, the sensitivity of sex reversal to elevated fry rearing temperature was wide between individuals within each population than across the three populations. Hence, sensitive individuals can be selected from the populations and their degree of sensitivity can be improved through continuous selection of progenies from temperature-sensitive parents

Fishes in the desert: mitochondrial variation and phylogeography of Danakilia (Actinopterygii: Cichlidae) and Aphanius (Actinopterygii: Cyprinodontidae) in the Danakil Depression of northeastern Africa

The Danakil Depression in northeastern Africa represents one of the harshest arid environments on Earth, yet two genera of fishes, Danakilia (Cichlidae) and Aphanius (Cyprinodontidae), share its sparse aquatic habitats. The evolutionary history of these fishes is investigated here in the context of genetic, geological and paleoenvironmental information. We collected samples from seven sites and assessed phylogeographic relationships using concatenated COI and cytb mtDNA genes. Danakilia morphospecies show low differentiation at mitochondrial markers, but variation is partitioned between a northern cluster containing D. dinicolai plus three undescribed riverine populations, and a southern cluster including two creek populations of D. franchettii separated by the hypersaline waters of Lake Afrera. Aphanius displayed four genetically distinct clades (A. stiassnyae in Lake Afrera; one distributed across the entire area; one in Lake Abaeded; and one in the Shukoray River), but without clear large-scale geographic structure. However, Danakil Aphanius are clearly differentiated from A. dispar sensu stricto from the Sinai Peninsula. Geological evidence suggests that after the Late Pleistocene closure of the Danakil-Red Sea connection, increased post-glacial groundwater availability caused the formation of a brackish paleolake flooding the entire region below the –50m contour. Fish populations previously isolated in coastal oases during glaciation were able to mix in the paleo-lake. Subsequently, in a more arid phase starting 7300 BP, paleo-lake regression isolated fishes in separate drainages, triggering their still ongoing diversification

Fishes in the desert: mitochondrial variation and phylogeography of <i>Danakilia</i> (Actinopterygii: Cichlidae) and <i>Aphanius</i> (Actinopterygii: Cyprinodontidae) in the Danakil Depression of northeastern Africa

<p>The Danakil Depression in northeastern Africa represents one of the harshest arid environments on Earth, yet two genera of fishes, <i>Danakilia</i> (Cichlidae) and <i>Aphanius</i> (Cyprinodontidae), share its sparse aquatic habitats. The evolutionary history of these fishes is investigated here in the context of genetic, geological and paleoenvironmental information. We collected samples from seven sites and assessed phylogeographic relationships using concatenated <i>COI</i> and <i>cytb</i> mtDNA genes. <i>Danakilia</i> morphospecies show low differentiation at mitochondrial markers, but variation is partitioned between a northern cluster containing <i>D. dinicolai</i> plus three undescribed riverine populations, and a southern cluster including two creek populations of <i>D. franchettii</i> separated by the hypersaline waters of Lake Afrera. <i>Aphanius</i> displayed four genetically distinct clades (<i>A. stiassnyae</i> in Lake Afrera; one distributed across the entire area; one in Lake Abaeded; and one in the Shukoray River), but without clear large-scale geographic structure. However, Danakil <i>Aphanius</i> are clearly differentiated from <i>A. dispar sensu stricto</i> from the Sinai Peninsula. Geological evidence suggests that after the Late Pleistocene closure of the Danakil-Red Sea connection, increased post-glacial groundwater availability caused the formation of a brackish paleo-lake flooding the entire region below the –50 m contour. Fish populations previously isolated in coastal oases during glaciation were able to mix in the paleo-lake. Subsequently, in a more arid phase starting ∼7300 BP, paleo-lake regression isolated fishes in separate drainages, triggering their still ongoing diversification.</p