A new copper (I) complex, [Cu(NN₁)₂](ClO₄)_, was synthesized, where NN₁ was a imine ligand 6-((quinolin-2-ylmethylene)amino)-2H-chromen-2-one obtained by a derivatization of natural compound coumarin. The structural characterization in solution was done by NMR techniques, UV-Vis and cyclic voltammetry. The potential antibacterial effect of [Cu(NN₁)₂](ClO₄)_, was assessed for F. psychrophilum isolated 10094. F. psychrophilum is a Gram-negative bacterium which causes diseases such as bacterial cold-water disease and rainbow trout fry syndrome, causing large economic losses in the freshwater salmonid aquaculture industry. This complex show to have antibacterial activity against F. psychrophilum 10094 at non-cytotoxic concentration in cell line derived from trout (F. psychrophilum 10094 IC₅₀ 16.0 ± 0.9; RT-GUT IC₅₀ 53.0 ± 3.1 µg/mL).

Previously, we reported an in vitro evaluation regarding antibacterial effects against F. psychrophilum by a new Cu (I) complex, [Cu(NN₁)₂](ClO₄). This study presents the results of an in vivo evaluation of [Cu(NN₁)₂](ClO₄) added as a dietary supplement against F. psychrophilum in rainbow trout. The results showed that the administration of [Cu(NN₁)₂](ClO₄) at 29 and 58 µg/g of fish for 15 days does not affect the growth of rainbow trout. On the other hand, the amount of copper present in the liver, intestine, and muscle of rainbow trout was determined. The results showed that the amount of copper in the liver, when compared between treated fish and control fish, does not change. While, in the intestine, an increase in the fish fed at 58 µg/g of fish was observed. In muscle, a slight decrease at 29 µg/g was obtained. Additionally, copper concentrations in the pond water after 15 days of feeding with the [Cu(NN₁)₂](ClO₄) complex showed the highest levels of copper. Finally, the effect of the administration of [Cu(NN₁)₂](ClO₄) for 15 days at 58 µg/g of fish was evaluated against F. psychrophilum, where a 75% survival was obtained during 20 days of challenge.

Piscirickettsia salmonis is the pathogen that most affects the salmon industry in Chile. Large quantities of antibiotics have been used to control it. In search of alternatives, we have developed [Cu(NN₁)₂]ClO₄ where NN₁ = 6-((quinolin-2-ylmethylene)amino)-2H-chromen-2-one. The antibacterial capacity of [Cu(NN₁)₂]ClO₄ was determined. Subsequently, the effect of the administration of [Cu(NN₁)₂]ClO₄ on the growth of S. salar, modulation of the immune system and the intestinal microbiota was studied. Finally, the ability to protect against a challenge with P. salmonis was evaluated. The results obtained showed that the compound has an MIC between 15 and 33.9 μg/mL in four isolates. On the other hand, the compound did not affect the growth of the fish; however, an increase in the transcript levels of IFN-γ, IL-12, IL-1β, CD4, lysozyme and perforin was observed in fish treated with 40 μg/g of fish. Furthermore, modulation of the intestinal microbiota was observed, increasing the genera of beneficial bacteria such as Lactobacillus and Bacillus as well as potential pathogens such as Vibrio and Piscirickettsia. Finally, the treatment increased survival in fish challenged with P. salmonis by more than 60%. These results demonstrate that the compound is capable of protecting fish against P. salmonis, probably by modulating the immune system and the composition of the intestinal microbiota.