Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare.

Henrike Seibel,Björn Baßmann,Alexander Rebl

doi:10.3389/fvets.2021.616955

Abstract

Blood analyses provide substantial information about the physiological aspects of animal welfare assessment, including the activation status of the neuroendocrine and immune system, acute and long-term impacts due to adverse husbandry conditions, potential diseases, and genetic predispositions. However, fish blood is still not routinely analyzed in research or aquaculture for the assessment of health and/or welfare. Over the years, the investigative techniques have evolved from antibody-based or PCR-based single-parameter analyses to now include transcriptomic, metabolomic, and proteomic approaches and from hematological observations to fluorescence-activated blood cell sorting in high-throughput modes. The range of testing techniques established for blood is now broader than for any other biogenic test material. Evaluation of the particular characteristics of fish blood, such as its cell composition, the nucleation of distinct blood cells, or the multiple isoforms of certain immune factors, requires adapted protocols and careful attention to the experimental designs and interpretation of the data. Analyses of fish blood can provide an integrated picture of the endocrine, immunological, reproductive, and genetic functions under defined environmental conditions and treatments. Therefore, the scarcity of high-throughput approaches using fish blood as a test material for fish physiology studies is surprising. This review summarizes the wide range of techniques that allow monitoring of informative fish blood parameters that are modulated by different stressors, conditions, and/or treatments. We provide a compact overview of several simple plasma tests and of multiparametric analyses of fish blood, and we discuss their potential use in the assessment of fish welfare and pathologies.

Highlights

A significant segment of the constantly growing aquaculture sector is represented by intensive farming practices [1] aimed at meeting the increasing demand of a growing world population
The Indian major carp (Catla catla) exposed to temperatures above and below the optimum temperature of 25◦C showed a significant increase in blood expression levels of immune genes coding for toll-like receptors (TLR2,−4,−5) and nucleotide binding oligomerization domain containing proteins (NOD1,−2) (Table 1) [74]
The increased expression of the genes coding for the transcriptional regulator high-mobility-group-box-1 protein HMBG1, the receptors TLR4 and NOD1, and their associated adapter proteins myeloid differentiation primary-response protein 88 (MYD88) and receptor interacting serine/threonine kinase 2 (RIPK2), as well as the cytokines IL6, CXCL8, and IL10 suggested an activation of early innate immune mechanisms by hypoxia (Table 1)

Summary

Introduction

A significant segment of the constantly growing aquaculture sector is represented by intensive farming practices [1] aimed at meeting the increasing demand of a growing world population. Many previous and current studies on fish welfare have measured the main components of the primary physiological stress response, largely plasma cortisol and glucose [26,27,28].

Results

Conclusion