Strong immunity is the first line of defence against stress and diseases. Research studies cite that this may be developed in fish through diet, biotics, fish oil replacement and inactivated vaccines.

Bridging the gap

Research advancements on probiotics, prebiotics and synbiotics have been guiding fish farmers toward responsible aquaculture. And there may never be enough of these for them.

A review article cited research gaps in the biotics and in understanding the role of synbiotics.

“This review highlights the gap between the knowledge of synbiotics and their practical application in aquaculture,” said author Muyassar H. Abualreesh, in “Effects of probiotics, prebiotics, and synbiotics on immune function, disease resistance, digestive health, and stress management in fish culture,” published in Frontiers in Marine Science.

Abualreesh, a professor at King Abdulaziz University, Jeddah, in Saudi Arabia, underscored the impact of synbiotics: it reduces environmental stress and promotes fish production in aquaculture.

“The use of synbiotics may reduce the application of antibiotics, thus reducing the accumulation of antibiotics or residues in fish muscle and preventing the development of drug-resistant microorganisms.

“In this context, this review would be useful for farmers to include synbiotics via feed or water to improve fish growth and minimize the environmental impact of aquaculture,” he said.

The study focused on current research advancements on the effects of probiotics, prebiotics, and synbiotics on antioxidant molecules, digestive enzymes, and stress mitigation effects in fish, shrimps and oysters.

Sending the right signals

Taurine influences innate immune responses and digestive function, and mTOR may play a role in regulating intestinal health in coho salmon.

This is the conclusion of a study in China which investigated the impact of dietary Tau on the interplay between digestive function, innate immune responses, and mTOR signaling in the small intestine of coho salmon (Oncorhynchus kisutch).

The study, “Effect of Dietary Taurine on the Innate Immune Responses, Digestive Function, and mTOR Signaling in Coho Salmon (Oncorhynchus kisutch),” was published on Aquaculture Nutrition.

mTOR has a crucial role in maintaining cellular health and function under oxidative stress conditions. In layman’s terms, it is “a protein inside the cells that acts as a central command switch for growth”.

Experimental diets were formulated to evaluate the effects of graded taurine level on the animal. Taurine (Tau) at 98 per cent purity was added to the basal diet at 0, 0.2, 0.4 and 0.6 g/kg to produce four experimental diets for coho salmon, each weighing about 5.4 g.

Fish in the control group were fed twice daily with 0.6 g/kg taurine diet to apparent satiation. Fish in mTOR inhibitor treatment group were fed with mTor inhibitor diet, which contains 20 mg/kg rapamycin, and 0.6g/kg taurine.

The fish were sampled two weeks later.

All experimental diets significantly increased the activity of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), which are three major anti-oxidant enzymes in animals.

“Among these, the diet containing 0.4 g/kg Tau resulted in the highest expression levels of CAT and GSH-PX,” they said. Additionally, diets with 0.2, 0.4, and 0.6 g/kg Tau significantly increased (p < 0.05) the expression of IL-1 gene.

“Similarly, all three Tau-supplemented diets markedly enhanced (p < 0.05) the expression of IL-6 gene. Furthermore, diets containing 0.2, 0.4, and 0.6 g/kg Tau significantly induced (p < 0.05) the expression of TNFα gene. These findings suggest that Tau exerts a broad stimulatory effect on the expression of cytokines involved in inflammatory responses,” said authors, Linxuan Bian et al.

IL-1β is a potent pro-inflammatory cytokine that plays a central role in innate immunity and inflammatory disease.

IL6 encodes a pro-inflammatory cytokine that integrates immune regulation, acute phase response, and metabolic homeostasis.

Tumor necrosis factor alpha (TNF-α) plays important roles in processes such as immunomodulation, fever, inflammatory response, inhibition of tumor formation, and inhibition of viral replication.

These findings suggest that the mTOR inhibitor exerts a suppressive effect on the expression of both antioxidant enzymes and immune cytokines involved in inflammatory responses, they said.

Fish oil replacement

Higher levels of argan oil replacement for fish oil have been found to have more benefits in juvenile rainbow trout.

The study in Turkey, “Dietary argan oil for juvenile rainbow trout: growth performance, fatty acid profile, and antioxidant defense,” assessed the replacement of dietary fish oil with argan oil at inclusion levels in juvenile rainbow trout (Oncorhynchus mykiss) over an eight-week feeding period.

Control diet was at zero per cent. Experimental were at 33, 67, and 100 per cent dietary replacement of fish oil.

All dietary treatments had no significant impact on the growth parameters, feed efficiency and proximate composition in the animal.

It was observed, however, that increasing argan oil inclusion resulted in a gradual reduction of long-chain n-3 polyunsaturated fatty acids in fish.

“The overall results suggest that argan oil can totally replace fish oil in the rainbow trout diet without compromising growth and feed utilization. It is noteworthy that the sustained growth and feed utilization at total replacement may be attributed to residual dietary n-3 LC-PUFAs provided by fishmeal and the relatively limited trial period.

“Therefore, to ensure sustainability over long-term feeding practices, partial replacement at 67 per cent is suggested, as this level enables fish to maintain comparable n-3 LC-PUFAs retention, optimal growth and feed utilization, and enhanced oxidative defense,” said authors, Chamae Said et al.

Virgin argan oil contains a higher total antioxidant capacity in comparison to other vegetable oils.

The study, published on Aquaculture International, focused on the potential of argan oil as partial fish oil substitute not only for its medicinal value but also for sustainability and environmental factors.

The highly resilient plant can be grown in arid and semi-arid conditions and has been used in efforts against desertification.

Per the authors, the study is a first on evaluating in juvenile rainbow trout the effects of dietary argan oil on hepatic oxidative stress responses.

Fight against TiLV

Inactivated whole-virus vaccine is capable of stimulating coordinated humoral and cellular responses against TiLV, based on the results of a study in India.

It assessed the protective efficacy of a cell culture-derived, formalin-inactivated whole virus vaccine for the Nile tilapia (Oreochromis niloticus) administered via injection or immersion.

In the study, titled “Evaluation of systemic and mucosal immune responses in Nile tilapia following intraperitoneal and immersion vaccination with inactivated tilapia lake virus (TiLV) vaccine,” mortality data were collected up to 28 days post-challenge (dpc).

Forty-nine out of 60 fish died in the control group. The highest mortality was observed at 10 dpc.

No mortality was observed in the vaccinated group. Noted though, were mild symptoms such as reduced feed intake, lethargy and redness in 17 of the 60 vaccinated fish, accounting for 28 per cent.

“The Kaplan–Meier analysis was performed and the survival curves were prepared for both the injection and immersion groups. The relative percent survival (RPS) was 100 per cent following injection vaccination and 83.88 per cent after immersion vaccination, demonstrating that both routes conferred substantial protective efficacy post-virus challenge,” said authors, Swatiprava Padhiary et al.

TiLV continues to be a major threat in the global tilapia industry. It could lead to as much as 90 per cent mortality rate, affecting fry, juvenile and adult. Disease prevention protocols include biosecurity, water quality management and early disease detection.

“However, these measures alone are not sufficient to control viral diseases. In this scenario, vaccination is widely recognized as a reliable and sustainable approach for long-term disease management in aquaculture. Inactivated vaccinations constitute the majority of commercially available viral vaccines in aquaculture,” the authors emphasized.

Inactivated vaccines, they said, are generally preferred for their stability, safety, ease of preparation and commercial viability.

The study was published on Nature.

Hatchery International

Message History

Delivery option(s)