Microscopic parasites intertwining with fish scales, representing the threat to fish health in aquaculture.

Silent Threat: How Parasites Impact Fish Health and Aquaculture

Jordan Keane in Health & Wellness August 2025 • 5 min read.

"Uncover the hidden dangers of monogenean infestations in fish farming and what it means for the future of sustainable aquaculture."

Aquaculture, the farming of aquatic organisms, faces numerous challenges, with disease being a primary concern. Parasitic infections, in particular, pose a significant threat to fish health and the overall productivity of aquaculture systems. These infections can lead to reduced growth rates, increased susceptibility to other diseases, and ultimately, economic losses for fish farmers.

One of the most common parasitic infections in fish is caused by monogeneans, a group of ectoparasites that primarily infest the gills and skin. While the impact of monogenean infestations can vary, severe infections can disrupt gill function, impair respiration, and trigger a cascade of physiological changes in the host fish. Understanding these changes is crucial for developing effective strategies to manage and mitigate the effects of parasitic infections in aquaculture.

This article delves into the specific effects of Thaparocleidus sp., a type of monogenean, on the health of Pangasianodon hypophthalmus, commonly known as Sutchi catfish or iridescent shark. By examining the haematological (blood-related) and biochemical parameters of infected fish, we can gain insights into the physiological consequences of parasitic infestations and identify potential biomarkers for assessing fish health.

Decoding the Impact: How Thaparocleidus Infestation Alters Fish Physiology

Microscopic parasites intertwining with fish scales, representing the threat to fish health in aquaculture.

A recent study investigated the impact of varying degrees of Thaparocleidus sp. infestation on the haematological and serum biochemical parameters of Pangasianodon hypophthalmus. The study revealed significant alterations in several key indicators, providing a clearer picture of how these parasites affect fish health. Here's a breakdown of the findings:

The research meticulously examined various blood components and serum enzymes in fish exposed to different levels of Thaparocleidus sp. The results indicated that even moderate infestations can trigger notable changes in the fish's physiology, with more severe infestations leading to even more pronounced effects.

Increased Erythrocyte and Haemoglobin Levels: Fish with moderate to high infestations showed significant increases in total erythrocyte count (TEC) and haemoglobin (Hb) levels. This may indicate the fish's attempt to compensate for reduced oxygen uptake due to gill damage caused by the parasites.
Changes in Blood Indices: The study also found significant decreases in mean cell volume (MCV) and mean cell haemoglobin (MCH) in moderately to highly infested fish, suggesting potential anaemia.
Elevated Leukocyte Count: The total leucocyte count (TLC) was significantly elevated in infested fish, indicating an immune response to the parasitic infection.
Altered Serum Enzyme Activity: The activities of serum glutamate oxaloacetate transaminase (SGOT), serum glutamate pyruvate transaminase (SGPT), and alkaline phosphatase (ALP) were significantly higher in infested fish, suggesting tissue damage and stress.
Increased Lactate and Bilirubin: Lactate dehydrogenase (LDH) activity and lactate levels, as well as serum bilirubin and creatinine concentrations, were also elevated in infested fish, indicating metabolic disturbances and potential kidney dysfunction.

These findings highlight the complex physiological changes that occur in fish as a result of monogenean infestations. The altered haematological and biochemical parameters reflect the fish's response to stress, tissue damage, and impaired organ function. These insights can be used to develop better diagnostic tools and management strategies for aquaculture.

Protecting Our Fish: Towards Sustainable Aquaculture Practices

The study underscores the importance of proactive measures to control and prevent parasitic infections in aquaculture systems. Regular monitoring of fish health, appropriate stocking densities, and effective biosecurity protocols are crucial for minimizing the risk of monogenean infestations and their associated consequences.

Furthermore, the identified haematological and biochemical markers can be used to develop rapid and accurate diagnostic tests for detecting parasitic infections in fish. Early detection allows for timely intervention and prevents the spread of the disease, reducing economic losses and promoting sustainable aquaculture practices.

By understanding the intricate relationship between fish, parasites, and their environment, we can develop innovative strategies to safeguard fish health and ensure the long-term sustainability of aquaculture, providing a reliable source of protein for a growing global population.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.exppara.2018.02.007, Alternate LINK

Title: Effects On Haematological And Serum Biochemical Parameters Of Pangasianodon Hypophthalmus To An Experimental Infection Of Thaparocleidus Sp. (Monogenea: Dactylogyridae)

Subject: Immunology

Journal: Experimental Parasitology

Publisher: Elsevier BV

Authors: Saurav Kumar, Ram Prakash Raman, K. Pani Prasad, P.P. Srivastava, Sanath Kumar, K.V. Rajendran

Published: 2018-05-01

Everything You Need To Know

What are monogeneans, like Thaparocleidus sp., and how do they impact fish health in aquaculture, particularly for species like Pangasianodon hypophthalmus?

Monogeneans, specifically Thaparocleidus sp., are ectoparasites that commonly infest the gills and skin of fish like Pangasianodon hypophthalmus. Severe Thaparocleidus sp. infestations can disrupt gill function, impair respiration, and trigger various physiological changes. Early detection and management of monogeneans is critical.

What specific haematological and biochemical changes occur in Pangasianodon hypophthalmus when infested with varying degrees of Thaparocleidus sp.?

In Pangasianodon hypophthalmus, Thaparocleidus sp. infestations led to increased erythrocyte and haemoglobin levels, decreases in mean cell volume (MCV) and mean cell haemoglobin (MCH), and elevated leucocyte count. Additionally, there were altered serum enzyme activities (SGOT, SGPT, and ALP) and increased lactate, bilirubin, and creatinine levels. These changes suggest the fish are experiencing stress, tissue damage, and impaired organ function. However, the specific response can vary based on the species of fish and the severity and duration of the infestation.

Why do erythrocyte and haemoglobin levels increase in Pangasianodon hypophthalmus infested with Thaparocleidus sp., and what does this indicate about the fish's physiological response?

Elevated erythrocyte and haemoglobin levels in Pangasianodon hypophthalmus infested with Thaparocleidus sp. likely indicate that the fish is trying to compensate for reduced oxygen uptake due to gill damage caused by the parasites. This is a physiological response to maintain oxygen supply to tissues when gill function is compromised. However, this compensation mechanism can only go so far and severe infestations can overwhelm the fish's ability to maintain adequate oxygenation.

What do elevated serum enzyme activities (SGOT, SGPT, ALP) and increased lactate, bilirubin, and creatinine levels signify in Pangasianodon hypophthalmus infested with Thaparocleidus sp.?

The increased activity of serum enzymes like SGOT, SGPT, and ALP, along with elevated lactate, bilirubin, and creatinine levels in Pangasianodon hypophthalmus infested with Thaparocleidus sp. suggests tissue damage, metabolic disturbances, and potential kidney dysfunction. SGOT and SGPT are indicators of liver damage, ALP can indicate liver or bone issues, while elevated bilirubin and creatinine suggest impaired kidney function. Lactate increase indicates a shift to anaerobic metabolism due to oxygen deprivation.

What are the key sustainable aquaculture practices that can help minimize the risk and impact of Thaparocleidus sp. infestations, and how can haematological and biochemical parameters be used for monitoring?

Sustainable aquaculture practices to minimize Thaparocleidus sp. infestations involve regular monitoring of fish health through haematological and biochemical parameters, maintaining appropriate stocking densities to reduce parasite transmission, and implementing effective biosecurity protocols to prevent the introduction and spread of parasites. Monitoring biomarkers like TEC, Hb, MCV, MCH, TLC, SGOT, SGPT, ALP, LDH, bilirubin and creatinine can help aquaculture farmers identify the start of Thaparocleidus sp. infestations.