# Looking for Greener Pastures: In Vitro Screening of Phytogenics for the Control of Sparicotyle chrysophrii in Gilthead Sea Bream

## TL;DR

This study tests plant-based compounds as alternatives to formalin for controlling a harmful gill parasite in sea bream, finding several effective and fast-acting options.

## Contribution

The study identifies new phytogenic compounds with strong in vitro efficacy against the gill parasite Sparicotyle chrysophrii.

## Key findings

- Several phytogenic active ingredients showed rapid and strong toxicity against S. chrysophrii with low LD50 values.
- Morphological damage was observed in parasites exposed to effective compounds, indicating direct parasiticidal effects.
- The identified compounds were effective at concentrations much lower than traditional formalin treatments.

## Abstract

The gill parasite Sparicotyle chrysophrii poses a significant threat to gilthead sea bream (
Sparus aurata
) aquaculture in the Mediterranean, causing considerable mortality and economic losses. As traditional chemotherapeutic treatments, like formalin, face growing regulatory restrictions, there is an urgent need for alternative control strategies. This study screened the in vitro antiparasitic activity of 16 phytogenic active ingredients (AIs), including essential oils (EOs) and commercial feed additives, against adult S. chrysophrii. Worms were exposed to a range of concentrations of each compound, and mortality was assessed over 24 h. Lethal dose 50% (LD
50) values were calculated and categorised by short‐, mid‐, and long‐term efficacy. Several AIs, such as
Cinnamomum zeylanicum
,
Origanum vulgare
,
Thymus vulgaris
, and the commercial formulations Arotec‐G and OA + HE+EO, demonstrated rapid and strong toxicity, with low LD
50 values observed within 2 h. In addition to lethality, characteristic morphological damage was detected in exposed parasites, indicating a direct and severe parasiticidal effect. These results highlight the high efficacy of various AIs at concentrations significantly lower than those used in standard formalin baths. Overall, the study identifies several promising candidates for the development of alternative treatments against S. chrysophrii, providing a solid scientific basis for future in vivo validation and integration into sustainable parasite control programs in marine aquaculture.