## 9 Impact of Micro and Nano Plastics Bioaccumulation on Blood Response in Fish  
In recent years, the investigation of blood parameters in fish have become of considerable importance and aroused enormous interest not only in aquaculture, but also in the evaluation of fish as organisms sensitive to anthropogenic pollutant load. In fish,the hematological and hematochemical parameters represent important laboratory indexes useful in the diagnosis of many diseases and therefore for the evaluation of the state of health [189; 190], physiological state of fish, food conditions, and quality of the water in which they live. The values of blood parameters provide useful information in various body processes and are of great importance in evaluating the harmful effects of anthropogenic pollution on aquatic environments. Fish live in intimate contact with the aquatic environment that significantly influences their blood homeostasis. In the past few years, there has been a significant increase of the experimental studies conducted in the hope of achieving a better understanding of the impact of micro- and nano-plastics (MP/NPs) on diverse organisms including fish. The fish homeostasis is altered by the exposure to polluting substances and materials of various kinds (including micro-nano plastics), causing a series of protective mechanisms such as changes in blood parameters [191; 192]. Therefore, the hematological and hematochemical parameters are useful bioindicators in evaluating the effect of different pollutants in fish [192]. In fish, the complete blood count or CBC (complete blood count), is a laboratory test of the blood (fast, inexpensive and practical) which contains all the information necessary for the evaluation of hematopoiesis [193]. The parameters evaluated are the following: WBC (white blood cells), RBC (red blood cells), Hb (hemoglobin), Hct (hematocrit), MCV (mean corpuscalor volume), MCH (mean corpuscalor hemoglobin), MCHC (mean corpuscalor hemoglobin concentration), and TC (thrombocytes). Currently, an improvement in the techniques of haematological investigations in fish has been achieved. New methods of blood analysis are now used routinely and applied in in the study of fish species. Two of these new techniques are represented by the hematological determination by means of an automated electronic system and by flow cytometry. The hematological determination in fish by automated method uses an electronic blood cell counter with an impendence analysis system. This apparatus was previously used for mammals and subsequently modified in the software to carry out the hematological analysis also in fish. For this purpose, a suitable fish lysing solution is used in the instrument. This method has been validated for various fish species [189; 194; 195; 196; 197]. Flow cytometry is one of the most modern analysis techniques for the detection and quantification of fish blood cells. It allows to identify, count, and characterize individual cells in mixed populations with rapidity and high precision [190]. These new diagnostic methods have brought great benefits to the veterinary medicine and to the study of fish haematology. Previous studies on various fish species, have shown a marked variation in haematological and hematochemical parameters due to exposure to various pollutants [184; 190; 189; 184; 190]. Among the various polluting substances and materials, MPs represent the most plentiful pollutants on Earth [200] due to their ubiquitous presence within the aquatic environment [201]. In the last years, the studies conducted to monitor the impact of MP/NPs on aquatic organisms have widely increased. A large variety of effects in various fish species were reported [128; 202]. Due to their small size, microplastics and nanoplastics can be ingested (directly or through the food chain) by fish. Once inside the body, the plastic particles mainly accumulate in the digestive tract and transferred to the circulatory system or to adjacent tissues [36], and can persist in the organism for a long time [203; 204; 205].