Increased ingestion and toxicity of polyamide microplastics in Nile tilapia with increase of salinity.

Microplastics pollution and salinity intrusion in freshwater ecosystem is one of the worldwide climate change consequences those have negative impacts on the physiology of aquatic organisms. Hence, a 15-day experiment was carried out where Nile tilapia (Oreochromis niloticus) was exposed to different salinity gradients i.e. 0 ‰, 3 ‰, 6 ‰, 9 ‰, and 12 ‰ alone and along with 10 mg/L polyamide microplastics (PA-MP) in order to measure its effects on the hematology, gill, and intestinal morphology. The results exhibited that all the fish treated with PA-MP ingested microplastics and the quantity of accumulation was significantly greater in higher salinity gradients (9 ‰ and 12 ‰). In addition, the PA-MP treated fish showed increased glucose level and at the same time reduced hemoglobin concentration with the increase of salinity. The percentages of abnormalities in erythrocytes both cellular (twin, teardrop and spindle shaped) and nuclear (notched nuclei, nuclear bridge and karyopyknosis) significantly enhanced with PA-MP exposure again in higher salinity treatments (9 ‰ and 12 ‰). The principal component analysis (PCA) exhibited that the addition of 10 mg/L PA-MP negatively affected the hematology of Nile tilapia than that of salinity treatments alone. Besides, the exposure of PA-MP in 9 ‰ and 12 ‰ salinity gradients escalated the severity of histological damages in gills and intestine. Overall, this experiment affirms that the increase of salinity enhanced the microplastics ingestion and toxicity in Nile tilapia, therefore, PA-MP possibly is addressed as additional physiological stressors along with increased salinity gradients in environment.

Size dependent ingestion and effects of microplastics on survivability, hematology and intestinal histopathology of juvenile striped catfish (Pangasianodon hypophthalmus).

Microplastic pollution is drastically increasing in aquatic ecosystems and it is assumed that different sizes of microplastics have diverse impacts on the physiology of aquatic organisms. Therefore, this study was intended to examine the ingestion and size specific effects of polyamide microplastic (PA-MP) on different physiological aspects such as growth, feed utilization, survivability, blood parameters and intestinal histopathology of juvenile striped catfish (Pangasianodon hypophthalmus). In a 28-day exposure, the fish were fed with different sized PA-MP with a concentration of 500 mg per kg of feed in order to simulate highly microplastic contaminated environment. Three different treatments were set for this experiment i.e. T1, 25-50 µm (smaller microplastic); T2, 300 µm-2 mm (larger microplastic); T3, (mixed) including a control (C); each had three replicates. The highest ingestion was recorded in the gastrointestinal tract (GIT) of fish exposed to smaller PA-MP treatments (T1 followed by T3). The results also showed compromised weight gain (WG; g), specific growth rate (SGR; %/day) and feed conversion ratio (FCR) with the exposure of PA-MP. Besides, survivability significantly reduced among treatments with the ingestion of smaller sized microplastic and found lowest in T1 (65.0 ± 5.0). In addition, the presence of PA-MP in feed negatively affected the concentration of hemoglobin and blood glucose. Similarly, smaller PA-MP caused most erythrocytic cellular and nuclear abnormalities; found highest in T1 that significantly different from other treatments (p < 0.05). Various histopathological deformities were observed in fish fed with PA-MP incorporated feed. The principal component analysis (PCA) showed that the toxicity and stress imparted by smaller PA-MP affected the survivability and blood parameters where larger PA-MP caused mild to severe abnormalities. Based on eigenvector values, the major abnormalities in intestine included occurrence of epithelium columnar degeneration (ECD: 0.402; PC1), hyperplasia of internal mucosa (HISM: 0.411; PC1), beheading of villi (BV: 0.323; PC1), atrophy of mucosa (AM: 0.322; PC1), tiny vacuoles in apical villi (TV: 0.438. PC2), crypt degeneration (CD: 0.375: PC2) and atrophy of goblet cell (AGC: 0.375; PC2). Therefore, it has been speculated that the size based PA-MP ingestion in the GIT interfered with the digestion and absorption as well as caused deformities that reflected negatively in survivability and hemato-biochemical parameters of juvenile striped catfish.