This study of the biodiversity of algae is the first interest in Yemen as a future vision for sustainable alternative solutions using sustainable resources as a sewage treatment plant with its channel length in Sanaa city, Yemen. The study aimed to screen the family of algal genera. A total of 13 samples were selected with GPS, and 100 ml of water was filled up in a plastic container and directly read as wet preparation under light microscope, identified in accordance with algae standard methods in three replicates with determination of temperature, pH, and total dissolved salts. The results showed that microalgae were conducted higher than others algae under the mean value of temperature 28C and neutral pH and high total dissolved salt, indicating the economical role of algae presence and waste treating by algae in despite of there was no physical or chemical processing treatment done, and the microalgae genus was found as Chlorella vulgaries with a ratio of 100%, followed by Chlamedomonas reinhardtii and Kirchneriella lunaries with a ratio of 76.72%, and the less found genus of filamentous algae was Nostoc sp., Oscillatoria phucus, Ulotrix micrasterias, Dingoflagellate ceratium, and Desmedium with a ratio of 7.69% for each, and finally, diatoms were found along the stages. The variant of the algal family will be used soon for many applications next studies.

The complete interneural insertion patterns were reported for the seven members of the genus Lethrinus (Lethrinidae) inhabiting the Red Sea coasts of the Republic of Yemen and compared with eight Lethrinus species obtained from different parts of the world. Over 190 specimens, representing 14 species of the genus Lethrinus, were used in the present study. The results showed that the pattern of the dorsal fin pterygiophores in anatomical relation to the vertebrae exhibits intraspecific stability. Therefore, it was possible to develop a key to differentiate the 14 Lethrinus species obtained from various parts of the world. Three supraneural spines were found in only 11 species, with three spines located anterior to the neural spine of the first vertebra.

Microalgae are thought to offer attractive biological platforms for the sustainable synthesis of biodegradable polymers, especially polyhydroxybutyrate (PHB), which belongs to the polyhydroxyalkanoate (PHA) family. Rapid and accurate screening techniques for finding high-PHB-producing microalgal strains are needed due to growing environmental issues related to traditional plastics. For the initial identification of intracellular polymer buildup, staining-based methods provide an economical and effective substitute for traditional analytical procedures. This study as first one achieved in Yemen aimed to evaluate and compare the performance of three staining approaches—Nile Red, Nile Blue A, and Sudan Black B—for the detection of PHB accumulation in microalgae. Nile Red was used for rapid visualization of intracellular hydrophobic compounds, while Nile Blue A was applied for more selective identification of PHB granules under optimized staining conditions. Sudan Black B provided complementary qualitative assessment of lipid and polymeric inclusions using light microscopy. In accordance to results reads above showed that the stain Nile Blue A dissolved in DMSO showed 100% to be the highest ratio of positive read followed by 98.2% of Nile Red dissolved in DMSO of positive read then 92.79% of Nile Blue A dissolved in Acetone of positive read after that 88.29% of Nile Red dissolved in acetone that showed as orange granules and finally 40.54% of Sudan Black B dissolved in ethanol as blue black granules to be the less ratio amongst all ones stains. However, as seen in the appendix's images, the negative findings revealed pink or red granules and cells. In calculating reads of samples the results showed out of 37 samples 32 samples are positive with 86.49% for biopolymer accumulating inside algal tested cells. These samples were selected to be used for other biotechnological application.

Microalgae are promising biological platforms for the sustainable production of biodegradable polymers, particularly polyhydroxybutyrate (PHB), a member of the polyhydroxyalkanoate (PHA) family. The environmental impacts of conventional plastics underscore the need for rapid, reliable screening methods to identify microalgal strains that accumulate PHB. Staining-based methods offer a cost-effective approach for the preliminary detection of intracellular polymer inclusions. This study, conducted in Yemen, compared three staining techniques—Nile Red, Nile Blue A, and Sudan Black B—for screening PHB accumulation in microalgal isolates. Nile Blue A was used to visualize putative PHB granules by fluorescence microscopy, Nile Red to detect intracellular hydrophobic inclusions, and Sudan Black B to provide a qualitative assessment by light microscopy. The findings indicate that the highest positive-reading rate was 100% for Nile Blue A dissolved in dimethyl sulfoxide (DMSO), followed by 98.20% for Nile Red in DMSO, 92.79% for Nile Blue A in acetone, and 88.29% for Nile Red in acetone. Sudan Black B in 70% ethanol yielded the lowest positive-reading rate (40.54%), with positive inclusions appearing blue-black. Negative reactions were characterized by pink or red cells or granules (Appendix A). Of the 37 samples examined in triplicate, 32 were classified as positive for intracellular biopolymer accumulation (86.49%). These samples may warrant further investigation for biotechnological applications. FTIR spectra of extracts from selected algal isolates showed absorption bands consistent with PHB, including an ester carbonyl (C=O) stretching band at approximately 1720–1724 cm⁻¹. These spectral features support the preliminary identification of PHB; additional confirmatory analyses are needed to establish polymer identity conclusively.