Essential oil use could reduce parasite load in farmed fish

Adding spiked pepper essential oil to the diets of farmed fish, may reduce parasite load and intensity, say researchers.

A team of researchers from several institutes in Brazil examined the potential for the essential oil (EO) generated from piper aduncum ​or spiked pepper to be incorporated into fish feed as a way of controlling the parasite Hysterothylacium sp.​ The group members published their results in the journal Aquaculture​​​.

“Therefore, in this study, the efficacy of the essential oil of P. aduncum in the control of the nematode Hysterothylacium sp. in pirarucu juveniles and its adverse effects on the metabolism of fish was assessed,”​ the researchers said.

The researchers found that the intensity and abundance of the parasites in the infected fish was lowered as more of the essential oil was added to the diet.

“The results confirm the anthelmintic effect of the essential oil of P. aduncum in the control of L3 larvae of the nematode Hysterothylacium sp. in pirarucu juveniles​,” they said. “This effect is due to the active principle of dillapiole, a substance that makes up >92% of the essential oil used in this study.”​

However, more work is needed to explore ways to improve the palatability of the ingredient, they added.

Why essential oil use?​

There has been increasing interest in commercial production of the pirarucu Arapaima gigas​, a fish species endemic to the Amazon region, the researchers said. However, there are obstacles remaining.

The fish species has challenges from mortality, especially during the initial phase of farming, they said. Fish losses are often attributed to infestation by or infection from pathogens and parasites.

Initial record of third-stage larvae of the parasite Hysterothylacium sp​ was found in the intestine, stomach and pyloric caeca of fish juveniles, they said.

“This nematode, when occurring at a high infection rate, can cause intestinal obstruction and lack of appetite in fish, causing significant economic losses in fish production; in addition, the presence of this nematode in food fish arises the concern to public health because of indications that it may present a zoonotic potential,”​ they added.

Larvae presence could trigger cellular and humoral immune responses and stimulate the immune system leading to allergies or gastrointestinal manifestation, they said.

Several chemicals have been used to control endoparasites and ectoparasites in fish, the researchers said. However, those practices have drawbacks including high cost, toxicity concerns and the possibility of resistance developing, along with risks for the environment.

Products derived from medicinal plants, however, have begun gaining prominence as an alternative, they said. “Brazil, which holds the largest floristic biodiversity of the planet and whose traditional population frequently uses medicinal plants for treating various diseases, is taking advantage of this potential to produce phytotherapeutic drugs in disease control in different sectors of animal production, including in fish farming,”​ they added.

The spiked pepper is among the plants of interest as it is widely distributed in the region and pharmacological effects of the essential oil have been linked to the ability to control pests and microorganisms.

It also appears to demonstrate insecticidal, bactericidal, acaricidal, molluscicidal, fungicidal and parasitical abilities, they said. “The essential oil of P. aduncum consists of monoterpene type hydrocarbons, sesquiterpene, and phenylpropanoids that are commonly found in species of the genus Piperaceae, and its concentration in leaves can vary from 0.25 to 4%,”​ they added.

Little is known about its efficacy and influence on the physiological homeostasis in fish, the researchers said.

Methods and materials​

During an initial palatability test, 60 fish were given one of five trial diets for a period of 7 or 15 days, the researchers said. The ingestion rate was calculated based on ingested feed and administered feed.

Diets were generated incorporating the EO at 0, 32, 48, 64 and 80ml/KG and then fed for 7 or 15 days, they said.

Fish were fed twice daily, with the supplemented or control feed given in the morning, the researchers said. Regardless of trial diet, all fish received an amount of non-supplemented feed in the second feeding.

The essential oil used in the trials was generated from collected leaves of the spiked pepper plant. A sample of the essential oil generated also was analyzed to determine its chemical compositions.

The essential oil was sprayed onto commercially produced feed pellet, to establish the diets, they said.  

In the feeding trial, fish were given one of five diets – a control and the control supplemented with 32, 48, 56 and 64ml/KG of the EO – for a 7 or 15 day period, the researchers said. At the end of the time periods, sample fish from each group were collected to check blood parameters and parasitological analysis.

Blood samples were taken and the anthelminthic efficacy was established, the researchers said. Fish also were collected to allow for parasitological analyses. Fish were harvested and their internal organs were collected for examination.

The parasite prevalence, average intensity, intensity and average abundances were established along with the EO efficacy, they said. Parasites also were identified.

Results​

Overall, the use of the EO was found to reduce parasite presence, the researchers said.

“At 7 and 15 days, the values of average intensity, average abundance, and intensity of parasites decreased with increasing EO concentration, and at 15 days, these were significantly lower between the treatment group and the control group, with an efficacy of 76.21% for 64 mL/kg​,” they said. “Thus, the EO of P. aduncum demonstrates anthelmintic potential in the control of nematode larvae in pirarucu without affecting fish homeostasis.”​

The evaluation of the essential oil found two primary substances dillapiole and trans-caryophyllene, they said.

The palatability trial found that fish receiving the feed with the largest amount of the EO had the lowest intake of the supplemented feed, the researchers said. “Furthermore, in the afternoon (use of feed without medication), although no decrease was observed in the intake rate, the animals presented lethargic behavior during food capture, which was not verified for the other concentrations,”​ they added.

It was determined that the highest concentration – 80ml/kg – of the EO made the feed less palatable for the fish, which reduced the ingestion of the supplemented feed, they said.

“For the efficacy tests, feed medicated containing up to 64 mL/kg essential oil of P. aduncum can be applied because ingestion at those levels did not differ significantly with the ingestion rate of the fish in the control group (without EO),” ​they said. “Furthermore, 100% fish survival was observed in 7 and 15 days of experimentation in all treatments.”​

In the efficacy test, blood parameters showed several changes after seven days they said. However, the glucose concentrations were not altered.

“Parasitological analysis revealed that, of the 135 examined fish, 100% were infested with nematode larvae in all treatment groups and at intensities that varied from 5 to 949 and 9 to 1221, in 7 and 15 days of the experiment, respectively, with no fish mortalities being observed,”​ the researchers said.

At 15 days, there were pronounced differences in parasite abundance and intensity between fish on the control and supplemented diets, and among fish on the diets supplemented at different levels, they said. Resulted of infestation improved linearly as more EO was added to the diet.

Source: Aquaculture​

Title: Control of Hysterothylacium sp. (Nematoda: Anisakidae) in juvenile pirarucu (Arapaima gigas) by the oral application of essential oil of Piper aduncum​

Authors: A Corral, M de Queiroz, S de Andrade-Porto, G Morey, F Chaves, V Fernandes, E Ono, E Affonso

DOI: doi.org/10.1016/j.aquaculture.2018.04.062​​