Trophic Interactions between Two Cichlid Species in Shatt Al-Arab River, Iraq

The diet composition and trophic relationships of the blue tilapia, Oreochromis aureus and redbelly tilapia, Coptodon zillii were investigated in the Shatt Al-Arab river from November 2015 to October 2016. Fishes were collected by gill nets, cast net and electro-fishing. The index of relative importance (IRI%) of food items was determined by combining the frequency of occurrence and points methods. There were monthly variations in feeding activity and intensity of both species, which decreased in the colder months. Both species were classified as herbivores. The main food items of O. aureus were macrophytes (44.3%), algae (31.4%), diatoms (9.3%), aquatic insects (6.6%) and detritus (6.3%). The diet of C. zillii is composed mainly of macrophytes (60.8%), algae (23.0%), detritus (8.6%) and diatoms (6.4). The trophic niche breadth values varied between 0.217 for C. zillii and 0.360 for O. aureus. The results demonstrated a high degree of dietary overlap between O. aureus and C. zillii, as both species fed on the same food sources

Polyculture of Largemouth Bass (Micropterus salmoides) with Blue Tilapia (Oreochromis aureus): Using Tilapia Progeny as Forage

In this study, five, 0.04-ha ponds were stocked with advanced size largemouth bass fingerlings at densities of 124, 247, 494, 988, and 1136/ha. Tilapia brood fish were stocked at densities of 590/ha (male: female ratio was 1:3). Pond trials were conducted for a 6-month period, June to December 1985. Bass survival ranged from 40 to 89%. Bass stocked at densities 494/ha (low density) grew significantly larger than those at 988/ha (high density). Mean bass weights and percent weight gains at harvest in low versus high density ponds were 593 g and 3,318% and 120 g and 329%, respectively. High density bass ponds produced larger tilapia broodfish at harvest. The number of juvenile tilapia surviving in low density bass ponds was substantially greater (20,000 juveniles/ha) than in high density bass ponds (99 and 420 juveniles/ha). The higher survival of tilapia juveniles in low density bass ponds was the apparent cause of significantly higher turbidity (determined from secchi disc measurements) in these ponds. The results of this study suggest that forage/predator ratios, based on densities of female tilapia broodfish to bass, of 0.7 and 1.4 are suitable for controlling spawn and producing large tilapia or for producing large bass, respectively.

Population Dynamics and Management of Invasive Blue Tilapia (Oreochromis aureus) in Garmat Ali River, Basrah, Iraq

The blue tilapia, Oreochromis aureus is an invasive species that has successfully established itself in most of the Iraqi waters. However, there is little information on the population dynamics of the species in these waters. Hence, the growth parameters, mortality rates, probability of capture, recruitment pattern and yield per recruit of blue tilapia in Garmat Ali River, Iraq was assessed using FiSAT II software. A total of 1664 blue tilapia fish were collected by different fishing gears from October 2019 to September 2020 for recording the relevant data. The length-weight relationship obtained was W=0.0147*L3.0748 for fish ranging from 7.5 to 26.3 cm total length suggesting that the species shows positive allometric growth. The asymptotic length (L∞), growth constant (K), theoretical age at zero-length (t0), growth performance index (Ø') and longevity (tmax) were 29.9 cm, 0.205, -1.293, 2.345 and 10.7 years, respectively. The total mortality (Z), natural (M), fishing (F) and exploitation (E) were 1.09, 0.61, 0.48 and 0.43, respectively. Length at first capture (L50) was found to be 13.92 cm. The main recruitment pulse was from March to July with a peak in April, which account for 18.4% of the total recruitment in the year. The relative yield per recruit analysis revealed that the present exploitation rate (Epresent) for blue tilapia was below than the biological target reference points (E0.1 and Emax), which denotes that this stock was not over-exploited. For management purposes, higher yields can be achieved by reducing the mesh sizes of the nets during fishing.

DNA FINGERINTS OF TILAPIA SPECIES IN SHATT AL-AREB RIVER USING RAPD MARKERS

In the last decade, tilapia fish species distributed in the Iraqi inland waters. Three species; Nile tilapia Oreochromis niloticus (Linnaeus, 1758), Blue tilapia Oreochromis aureus (Steindachner, 1864) and Redbelly tilapia Coptedon zillii (Gervais, 1848) inhibiting Shatt Al-Arab River. They belong to family Cichlidae. They are very similar to differentiate among them using biometry. So, genetic markers used for species discrimination. Randomly amplified polymorphic DNA (RAPD) protocol used to examine genetic variation and to generate DNA fingerprints of tilapia fish species in Shatt Al-Arab River. Sixty-two specimens of tilapia fish collected from Shatt Al-Arab River at the governorate of Basrah. Seven universal decamer primers selected (OPA08, OPA10, OPA13, OPA17, OPA19, OPB08 and OPC02) to create RAPD DNA fingerprint. RAPD-PCR amplification carried out and electrophoresed with 100 bp ladder. DNA bands scored and molecular weight was calculated using PhotocaptMW software. Analog histogram drew using MS-Excel. The three RAPD DNA profiles apparently were different. DNA bands scored in the three species were 67 bands. The size of DNA bands was ranged from 64 bp to 2344 bp. RAPD fingerprints were efficient to distinguish the three species of tilapia fish. DNA markers of the three species of tilapia fish can use to achieve conservation programs of fish species in the future.

EVALUASI PERFORMA PERTUMBUHAN DAN HETEROSIS PERSILANGAN ANTARA IKAN NILA NIRWANA (OREOCHROMIS NILOTICUS) BETINA DENGAN IKAN NILA BIRU (OREOCHROMIS AUREUS) JANTAN F2 PADA KONDISI TAMBAK HIPERSALINITAS

Srikandi Tilapia is one of the superior hybridized varieties between black tilapia (Oreochromis niloticus) and blue tilapia (Oreochromis aureus). This fish has fast growth and high salinity tolerance. In its development, efforts are needed to improve and improve its genetic quality. Spawning srikandi tilapia using the parent of male blue tilapia F2 (family selection) is expected to improve performance better than the previous generation.The purpose of this study was to evaluate the growth performance and heterosis value of Srikandi tilapia produced from the extraction of female Nirwana strain tilapia with male blue tilapia F2. Hatchery activities were carried out in freshwater by mass spawning method on the 25 m2 pool. Enlargement activities were carried out at brackish water pond with salinity 25–40 g / L, using net measuring 3×5×1 m3 for 120 days. The stocking density used is 15 fishes / m2. The results of this study indicate that at the final test, the hybridization of Nw ♀x Au (F2)♂ has the best performance with the average of long gain16.60 ± 0.41cm, weight gain 215.33 ± 12.19 g and survival rate 78.50 ± 02.12. Evaluation of heterosis values on the characters of length, weight, survival, and biomass showed a positive value both on the hybridization of Nw ♀x Au (F2)♂ and Au (F2)♀x NW♂. The highest high parent heterosis value for blue tilapia broodstock is shown by population Nw ♀x Au (F2)♂ with values in each character of 6.96% (length), 26.06% (weight), 2.63% (survival), 28.57% (biomass).

High-quality chromosome-level genomes of two tilapia species reveal their evolution of repeat sequences and sex chromosomes

BackgroundTilapias are one of the most farmed fishes that are coined as ‘aquatic chicken’ by the food industry. Like many other teleosts, Nile tilapia and blue tilapia exhibit very recent transition of sex chromosome systems since their divergence about 5 million years ago, making them a great model for elucidating the molecular and evolutionary mechanisms of sex chromosome turnovers. Studies into their sex-determining pathways are also critical for developing genetic sex control in aquaculture.ResultsWe report here the newly produced genomes of Nile tilapia and blue tilapia that integrate long-read sequencing and chromatin conformation data. The two nearly complete genomes have anchored over 97% of the sequences into linkage groups (LGs), and assembled majorities of complex repetitive regions including telomeres, centromeres and rDNA clusters. In particular, we inferred two episodes of repeat expansion at LG3 respectively in the ancestor of cichlids and that of tilapias. The consequential large heterochromatic region concentrated at one end of LG3 comprises tandem arrays of mRNA and small RNA genes, among which we have identified a candidate female determining gene Paics in blue tilapia. Paics show female-specific patterns of single-nucleotide variants, copy numbers and expression patterns in gonads during early gonadogenesis.ConclusionsOur work provide a very important genomic resource for functional studies of cichlids, and suggested that unequal distribution of repeat content that impacts the local recombination rate might make some chromosomes more likely to become sex chromosomes.

Analysis of the Biological Features of the Blue Tilapia, Oreochromis aureus in the Garmat Ali River, Basrah, Iraq

The blue tilapia, Oreochromis aureus (Steindachner, 1864) is exotic fish and became widely distributed throughout different natural waters of Iraq during the last years. The present study describes the length compositions, age, growth, reproduction and food habit of the species in the Garmat Ali River from September 2018 to August 2019. A total of 1050 specimens were caught using gill nets, cast net, and electro-fishing. The lengths of O. aureus ranged from 6.6 to 22.9 cm, and the most dominant lengths were 14.0 to 18.0 cm representing 61.6% of the catch. A positive allometric growth pattern was observed for males (b= 3.317), females (b= 3.231) and all individuals (b= 3.283). There were three peaks for relative condition factor (Kn) that appeared during October, April, and July for both sexes. The age estimated on the basis of scales showed that the population comprised of 1 to 5 years. The parameters of the von Bertalanffy growth curve were L∞= 27.6 cm, K= 0.193 and to= 1.18. The growth performance index (ø) of O. aureus was computed as 2.17. The overall sex ratio (male: female) was1:1.04. Females attained sexual maturity at a lower size than males with mean size at first maturity determined as 6.6 cm for females and 9.2 cm for males. Two peaks of the gonado-somatic index were shown, the higher one in April and the lower one in September in both sexes. The estimated fecundity ranged from 352 to 1033 eggs in the fish ranging from 12.2 to 20.5 cm in length. O. aureus is an opportunistic feeder that will successfully utilize whatever food source is available, its diet comprised of detritus (43.1%), diatoms (23.9%), algae (22.8%), macrophytes (7.1%) and crustaceans (6.0%). The results highlighted basic biological features on invasion fish species which can assist in fisheries management and conservation of the fish species in Iraqi waters.