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Microorganisms colonize plastics in the aquatic environment but their composition on plastics used in aquaculture remains poorly studied. Microorganisms play a significant role in aquaculture in terms of water quality and the health of cultivated species. In the current study, we explored the composition of microorganisms on floating plastics and their surrounding water collected from ponds and open aquaculture areas. Using scanning electron microscopy, the diversity of microbial communities, primarily diatoms, and bacteria were identified on the plastic surfaces. Additionally, epifluorescence microscopy revealed that prokaryotes were colonized on all plastic samples from 0.1 to 29.27×103 cells/cm2, with a high abundance found in open aquaculture areas compared to ponds. Bacterial communities were characterized by 16S rRNA sequencing which showed that bacterial communities on plastics were dominated by Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria. The level of these microbial communities on the plastics differed from those found in the surrounding seawater samples and the abundance of potentially pathogenic bacteria was higher in plastics than in seawater samples. Moreover, hydrocarbon-degrading bacteria were more abundant in the investigated plastic samples than in the water samples. This study contributes to the knowledge regarding the plastisphere community in aquaculture.

The objective of this study was to evaluate the effect of graded levels (0.0 , 2.5, 5.0 and 7.5g /kg diet ) of the dietary blue-green microalgae (Spirulina) Arthrospira platensis as feed supplement to assess growth performance , nutrient utilization, immune response , some hematological parameters, and proximate composition of the Nile tilapia (O. niloticus) . A completely randomized experimental design was developed with 4 treatments and two replicates . Fish (80 all-male Nile tilapia fingerlings) ,with an average initial weight of 6±0.20 g , were randomly distributed into 8 glass aquaria (112 liter) and each aquarium holding 10 fish and randomly assigned to one of two replicates of the diets and offered feed to satiation to fingerlings O. niloticus. Fish were fed a balanced diet of 30% protein along the period of the experiment. The treatments were Diet 1 (Control) without Spirulina, Diet 2 (2.5g Spirulina /kg diet), Diet 3 (5g Spirulina /kg diet) and Diet 4 (7.5 g Spirulina /kg diet ). The results indicate that, the fish groups received Spirulina supplemental diets revealed significant improvement in growth parameters (body weight gain, feed conversion ratio and protein efficiency ratio). Since the diets contained microalga Spirulina at a level (7.5 gram/kg diet) showed the highest values of growth parameters and protein utilization. Carcass composition of the experimental fish was relatively affected by different dietary treatments. This study suggested that Spirulina at a level of 7.5 gram/kg can be used in the feed of Nile tilapia without negative effect on growth parameters, feed utilization and blood parameters.