Using fish blood as a bio-indicator to examine their response to environmental conditions

The speed of urbanization and industrialization in areas near the sea is always proportional to the pressure on the environment. Untreated waste from factories in industrial zones becomes the main source of pollution to natural water, including aquaculture water systems. Heavy metal or toxic chemical pollution is the major threat to aquatic life, including fish. At high concentrations, heavy metals are lethal to aquatic organisms, and at sub-acute concentrations, they gradually accumulate in organisms and along the food chain. The dangers of heavy metals to human health only become apparent when people use aquatic organisms, including fish, for daily food.

The Project entitled "Evaluating morphological characteristics of blood cells and hematological parameters of common fish species in the Central sea area (Ha Tinh) at risk of pollution due to waste discharge", conducted by the research team of the Tropical Ecology Institute of, Vietnam - Russia Tropical Center. The objective of the project is to assess the effects of environmental pollution on fish blood cell morphology and some biochemical indicators of fish species both in the natural environment and in caged fish with economic values in three areas, including two in Ha Tinh and one in Nha Trang.

In recent years, fish hematological and biochemical indicators have become promising biological indicators in measuring the impact of water pollution on fish as the blood indicators are very reactive to pollutants. The study of fish hematological changes under polluted conditions and the use of fish blood as bio-indicators in fisheries has developed quite rapidly as it is very important for toxicity studies, environmental monitoring, and prediction of the health status of fish.

Within the scope of the project, the researcher analyzed the contents of heavy metals in water such as Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg, and Pb at three locations: one is an estuary within 5 nautical miles of Vung Ang Industrial Zone (Ky Anh, Ha Tinh); another is an estuary with flows from residential and urban areas pouring into the sea (Thach Kim, Ha Tinh); and the last is related to both tourism and aquaculture activities (Nha Trang, Khanh Hoa). The results showed that the water quality at the three study sites was within the allowable limits under to the Ministry of Natural Resources and Environment’s National Technical Regulations on Sea Water Quality for Aquaculture (QCVN 10-MT:2015/BTNMT).

In terms of biology, in addition to obtaining valuable data on the hematological profiles of the studied fish species, the researcher also discovered remarkable characteristics of the red blood cell morphology of the caged fish and wild fish. Although they were caged fish, red blood cells of Sciaenops ocellatus had obvious morphological abnormalities. Disorders included asymmetrical cell shape, wrinkled membrane structure, uneven distribution of nuclear material (chromatin), and asymmetric nuclear shape. Especially, the morphological disorder, unequal distribution of nucleus, and unbalanced nucleus shape accounted for a high proportion, with areas up to 83% and 87% respectively (Figure 1). Lates calcarifer and some wild fish such as Mugilidae sp., Decapterus sp., Epinephelus fuscoguttatus, Aluterus monoceros, and Pampus argenteus, showed a very low level of red blood cell disorder, only 0 - 1% (Figure 2. This is the level observed in most fish species living under normal environmental and nutritional conditions. The expression of red blood cell morphology disorder in fish has been recorded by researchers around the world in locations related to habitat pollution due to heavy metals, organic and inorganic toxins, insecticides etc. The response of each fish species is not the same and is species-specific. Some species exhibit sensitivity to environmental conditions, while others show greater tolerance and less sensitiveness.

Figure 1. Red blood cells of red snappers in fish cages. a – caged fish blood in Loc Ha (Ha Tinh), b – caged fish blood Ky Anh (Ha Tinh), c – caged fish blood in Nha Trang (Khanh Hoa). Red arrows indicate red blood cell nuclei deformed/uneven nuclear distribution, while blue arrows indicate mild basophilic red blood cells.

Figure 2. Red blood cells of some fish species. a - Mugilidae sp. (L1.4), b - Decapterus sp. (L1.4), c -Epinephelus fuscoguttatus (L2.1), d - Scatophagus argus (L3.4), e - Aluterus monoceros (L3.6), and f - Pampus argenteus (L3.6).

The data obtained by the project showed that, although the water quality at the study locations ưas within the allowable limits, their synergistic effects, even in small amounts, caused different responses to the fish body at the cellular level, and, in certain cases, some species showed a very strong response to environmental factors - for this project, red snapper Sciaenops ocellatus, one of the most popular commercially farmed fish in many central coastal provinces. The negative impact of environmental conditions on fish bodies could lead to effects on fish quality, growth, and development and reduce economic efficiency in calculation of commercial values of the people and investors.

Part of the project findings has been published in two international articles:

1. Quyet D.H. Blood cells and some hematological parameters of red drum (Linnaeus, 1766) in Vietnam. Brazililan Journal of Biology. 86.6. 2021. (ISI, H-index = 49, IF = 1,2).

2. Quyet D.H., Thuy Duong H.T., Chernyaskikh S.D., Tinh P.H., Dat T.V., Tu N.T. Red blood cell morphology of some fish species in Ha Tinh and Nha Trang, Vietnam. Ecology, Environment and Conservation. May 2021 Supplement Issue. (Scopus, H-index = 16).

Article and photo by Dr. Do Huu Quyet/Institute of Tropical Ecology