Egyptian Journal of Aquatic Research最新文献

Since natural coagulants are readily available, inexpensive, nontoxic, and biodegradable, they are now proving to be effective alternatives to chemical coagulants. This research article investigates the potential of de-oiled peanut (Arachis hypogaea) seeds as a natural coagulant for surface water treatment, comparing its effectiveness with alum, a widely-used chemical coagulant. Ten surface water samples were obtained from the Nile River in the greater Cairo region and treated using coagulants – peanut seeds and alum. Key parameters, such as turbidity, chemical oxygen demand (COD), total bacterial count (TBC), Escherichia coli, and enterococci, were measured to assess the coagulation efficiencies of both substances. Results revealed a minor disparity in turbidity removal, with peanut seeds achieving 75.4% to 85.0% removal, while alum exceeded 90.0%. A more pronounced difference in COD removal was observed, as peanut seeds exhibited a 41.7–53.2% removal rate, in contrast to alum’s maximum removal of 92.3%. Regarding bacterial removal efficiency, alum demonstrated a slightly superior performance (60.0–70.0%) compared to peanut seeds (approximately 50.0%). In conclusion, de-oiled peanut seeds represent an affordable and environmentally friendly alternative coagulant for surface water treatment.

The present study was carried out to evaluate the growth pattern and population status of the sea urchin Paracentrotus lividus (Lamarck, 1816) in the Egyptian Mediterranean coast off Alexandria City. A total number of 2575 specimens were collected from their fishing grounds during 2017 to 2018. The size classes ranged from 9–57 mm with a mean value of 34.27 mm. Classes from 27 to 41 mm represented about 81.44% of the total collected catch. The length-weight relationship (W_t = 0.0039 L^2.3839) reflected a pattern of negative allometric growth. Age was determined using the Bhattacharya’s method based on the length frequency data. Six age or cohort groups were recognized. The Von Bertalanffy growth equations for length and weight were found to be L_t = 71.17[1 – e^{-0.215(t +0.130)}] and W_t = 102[1 – e^{-0.215(t +0.130)}]^2.3839. The estimated longevity t_max for the Egyptian urchin was 13.96 years. The growth indices for length and weight were Φ’_L = 3.04 and Φ’_Wt = 0.67. The values of total mortality (Z), natural mortality (M), and fishing mortality (F) were 1.767, 0.47, and 1.297, respectively. The Egyptian urchin population showed an exploitation ratio of 0.73, indicating an over-exploitation status. The results of the yield per recruit and the relative yield per recruit emphasized the urgent need of fishery management strategies to control the fishing practices of the edible purple sea urchin P. lividus for future sustainability of its wild population off the coast of Alexandria. Further work is also needed to investigate other P. lividus populations along the Egyptian Mediterranean coast and assess their health status.

This study investigates the growth pattern of 33 fish species caught by gillnets from the Egyptian Mediterranean waters off Alexandria between 2018 and 2020. This is accomplished by studying the length-weight relationship (LWR), Fulton’s condition factor (k_c), the allometric condition factor (k_a), and the relative weight condition factor (k_n). The b-values of the length-weight relationship of the studied species varied between 2.1382 and 3.6868 according to the results. Only Dentex macrophthalmus (b = 2.1382), Etrumeus golanii (b = 2.4197), and Trichiurus lepturus (b = 3.6868) exhibited different values than the expected range of 2.5 < b less than 3.5. The 95 % confidence interval (CI) and Bailey’s t-test of b-values were tested. In terms of growth pattern, the results showed 20 fish species with an isometric growth pattern, 10 fish species with negative allometric growth, and only 3 fish species with positive allometric growth. The study of Fulton’s condition factor (k_c) assessed the differences between species to the differences in fish shape, and proposed that each fish family has its own range depending on the fish shape, and (k_c > 1) is not necessarily a better condition for the fish. The study of the allometric condition factor (k_a) assessed that the difference between k_a and k_c values influenced by the feeding intensity and the b-value. The values of the relative weight condition factor (k_n) were within the range from 0.929 to 1.038, and 24 fish species reflected a good growth condition while the k_n values for the remaining 9 species were less than 1.0. The obtained results add new data about specific species and provide updated data on the remaining species in the area of study. The obtained results can have useful effects on the stock assessment of fish species.

Groins are one of the most important facilities used to protect coastal regions. In this research, groins made from a concrete cube were tested experimentally. This research investigates the impact of groin length (Lg) of 105, 135, and 165 cm and groin angle with the normal axis of the shoreline (θ) of 0^°, 10^°, 20^°, and 30° under different dimensionless wave numbers (khg), from 0.34 to 1.26, with the beach slope of 8:1. The units used to indicate erosion and deposition are dimensionless erosion depth (Smax/h), dimensionless deposition height (Dmax/h), and dimensionless erosion hole length (lsmax/h). The sandy bed changes and wave reflection from the groin were monitored. The results showed that the angle of 30° had more impact on beach stability than that of 0°, and more sediments were eroded by short groins than by long ones. The reflection of waves from groins was also studied as a function of the reflection coefficient (kr). As concluded, short groins reflect higher waves than long ones.

The effects of utilizing green seaweed (Cladophora sp.) and red seaweed (Gracilaria tenuistipitata) as a shelter in the nursery rearing of juvenile mud crabs (Scylla paramamosain) at different stocking densities were investigated for 3 weeks. The investigation comprised a 3 × 2 factor with three stocking densities (200, 300, and 400 ind/m²) combined with two types of seaweed (green seaweed and red seaweed) randomly allocated in triplicate tanks. Juvenile crabs (0.81 ± 0.09 g) were stocked in 150-L tanks (tank bottom area: 0.3 m²) at a salinity of 15  ppt with constant aeration. Crabs were fed twice daily with frozen Artemia biomass. The findings revealed that the survival and growth rate of crabs did not significantly respond to the combined effects of seaweed type and stocking density (P > 0.05). Crabs reared at a low density (200 ind/m²) grew faster than those reared at a high density (400 ind/m²), while seaweed type did not affect crab growth rates. Moreover, crab production increased noticeably as stocking density increased and was significantly influenced by the interaction. The highest crab production was found in the 400 ind/m² treatment with red seaweed as shelter when compared to other treatments (P < 0.05), indicating that this seaweed species is an ideal shelter for rearing juvenile crabs at high density.

Clay minerals such as bentonite (BNT) have recently drawn attention as non-nutritive additives in aquaculture, which can maintain water quality and maximize productivity. As water additives, four levels of natural BNT—0, 1.5, 3, and 4.5 g/liter (‰)—were evaluated. Juvenile European seabass (Dicentrarchus labrax) were stocked in fiberglass tanks and fed a commercial diet of 46/16 (protein/fat) for 56 days. The results showed that the BNT-treated groups had significantly reduced NH₃ content (p < 0.05) than the control group. Fish performance improved significantly in the BNT-treated groups. Blood biochemistry, digestive enzymes, liver and kidney function improved significantly with increasing BNT levels, in addition to the improvement of immune and antioxidant parameters, i.e., IGM, cortisol, MDA, catalase, TAC, and GPx, in comparison to the control group. Data on the gills, intestine, and stomach histology showed that the BNT-treated groups had healthier organs. However, the liver histomorphology reveals that hepatic vacuolations did not improve in the BNT-treated groups with the exception of the B3 group. Besides, pancreatic sections were normal in all BNT-treated groups. Therefore, natural BNT can be recommended for application in marine aquaculture at a level of 3 g/L, to reduce ammonia and improve fish growth, health and immunity.

The Nile Delta coast extends along the middle region of Egypt’s Mediterranean coast, from Port Said eastward to Alexandria westward. Six short sediment cores were collected across the Nile Delta sector to assess the pollution level of nine heavy metals: Fe, Mn, Zn, Ni, Cu, Cr, Cd, Pb, and Ba. Geochemical analysis of the core samples revealed their sediment features. The predominant sediment was Nile fine-grained sand, with fluctuations in organic matter, carbonate, and heavy metal content. They correspond mainly to an exposure scale to effluent discharges, relevant to anthropogenic factors influencing the coastal ecosystem. The applied environmental indices demonstrated that the western and middle sites of the Nile Delta are classified as unpolluted areas, while the eastern edge, represented by the Port Said core, is identified as polluted area. Variations in the metal contamination level were recognized, ranging from high contamination with Cd to considerable contamination with Cr, and moderate contamination with Zn, Ni, Cu, Mn, and Fe. Port Said site is significantly affected by the anthropogenic impact of industries and port activities. It is recommended to mitigate ecological threats and limit pollution spreading westward to prevent further degradation of the Nile Delta coast.

This study presents the first record of a spiny eel species from the family Mastacembelidae in the Nile Delta region of Egypt, where this family was previously thought to be absent except in the Aswa River and Lake Victoria. Morphological and molecular methods were employed to confirm the identification of the newly identified species, based on seven collected specimens. Morphometric and meristic characters were used to compare the new species with other African and Asian Mastacembelidae and confirm its geographic distribution. In addition, molecular markers were used to further confirm the identification of mitochondrial genome [Cytochrome oxidase subunit I (COI), Cytochrome b (Cyt b), and D- loop], in integration with one nuclear marker [the first intron of the ribosomal nuclear marker S7 (RPS7)]. Results indicate that the newly reported species belongs to the genus Mastacembelus and is a close relative of Mastacembelus frenatus. This report of a new African species in the River Nile Delta expands our understanding of the geographical distribution range of the Mastacembelidae family.

A total of 300 freshwater mussels Lamellidens marginalis were sampled from the Ratargul Freshwater Swamp between December 2020 and November 2021 to investigate the relationships between length, weight, soft tissue wet parameters, sex ratio, condition indices, gonadal histology, and hydrological features of swamp forest habitat. The shell length and shell weight varied between 5.00 and 9.50 cm and 12.26–78.96 g respectively. The length at maturity L_m was recorded as 5.98 cm and the calculated value of χ² suggested a dominant female stock at the study site (P < 0.05). The relationship between different morphometrics of Lamellidens marginalis and environmental parameters exhibits a very weak regression coefficient value (P < 0.05), suggesting a weak effect of seasonality on the growth metrics. Previtellogenic and vitellogenic oocytes were observed in the ovary, and mature spermatids were found in the testes in samples collected in the rainy season.

Increased demand for the production of sharks in the Arafura Sea can lead to the overfishing condition, which resulted in the depletion of fish stocks. Effective management measures are crucial to ensure the sustainability of shark fisheries. The objectives of this study were to investigate the stock status and to recommend some management strategies for shark fisheries in the Arafura Sea. Length frequency data and some life history parameters were used to perform a length-based stock assessment of Carcharhinus sealei in the Arafura Sea. C. sealei has an asymptotic length of 102.25 cm with a growth constant of 0.36 year⁻¹. C. sealei has been exploited heavily, which was indicated by the current fishing mortality (F_cur = 1.2 year⁻¹), which was much higher than its natural mortality (M = 0.29 year⁻¹) and the optimal fishing mortality (F_40%=0.49 year⁻¹). This study revealed that the high fishing pressure of sharks has resulted in the stock overfished condition for C. sealei in the Arafura Sea, with the current spawning potential ratio (SPR_cur = 0.23) less than the reference point 40% SPR. The low selectivity of drift gillnet (current Lc₅₀ = 66 cm) caused the low spawning stock biomass of C. sealei. The stock rebuilding strategy would be required to increase the spawning stock biomass of C. sealei. A minimum legal size of 77 cm, a marine protected area, and effort controls were some management strategies that can be adopted for the sustainability of shark fisheries in the Arafura Sea.