Use of substituted heterocyclic compounds to control sea lice on fish

A method of controlling sea lice in and on fish, which comprises treating the sea lice with an active substance, said active substance a compound of formula

• including all geometric and stereoisomers, N-oxides, S-oxides and salts thereof,
• wherein, R′, R″ and R′″ are each independently hydrogen, halogen, cyano, C1-C2-alkyl, halo-C1-C2-alkyl, C1-C2-alkoxy or C1-C2-haloalkoxy, subject to the proviso that at least one of R′, R″ and R′″ is not hydrogen;
• A1 is C, A2 is N, A3 is O, CH2 or NR1′ and the bond between A1 and A2 is a double bond;
• or A1 is N, A2 and A3 are each CH2 and the bond between A1 and A2 is a single bond;
• R1′ independently is as defined as R1 below;
• and X is
• (a) a radical of formula
• wherein R5 is C1-C2-haloalkyl, halogen, nitro or cyano and Q is
• (i) a 5- or 6-membered heteroaromatic ring comprising 1 to 3 same or different heteroatoms selected from the group consisting of O, S and N;
• or is
• (ii) a group —C(O)N(R1)-T, wherein R1 is H, C1-C4-alkyl, C2-C4-alkylcarbonyl or C2-C4-alkoxycarbonyl and T is C1-C6-alkyl which is unsubstituted or substituted by C3-C6-cycloalkyl, halogen, cyano, nitro, amino, hydroxy, C1-C6-alkoxy, C1-C6-haloalkoxy, C1-C6-alkylthio, C1-C6-haloalkylthio, C1-C6-alkylsulfinyl, C1-C6-haloalkylsulfinyl, C1-C6-alkylsulfonyl, C1-C6-haloalkylsulfonyl, carboxy, carbamoyl, C1-C6-alkylcarbonylamino, C1-C6-haloalkylcarbonylamino, C1-C6-alkoxycarbonyl, sulfonamido, N-mono- or N,N,di-C1-C4-alkylsulfonamido, C2-C6-alkanoyl, unsubstituted or in the alkyl portion by halogen, cyano, ethenyl or ethynyl substituted N—C1-C6-alkylaminocarbonyl, or unsubstituted or halogen-, C1-C2-alkyl-, C1-C2-haloalkyl or cyano-substituted 4- to 6-membered heterocyclyl;
• or T is C3-C6-cycloalkyl or 4- to 6-membered heterocyclyl, which is each unsubstituted or substituted by halogen, C1-C2-alkyl, C1-C2-haloalkyl or cyano;
• or is
• (iii) a radical —C(O)NH—C═N—O—C1-C2-alkyl, a radical —C(O)N═C—N-di-C1-C2-alkyl or a radical —C(O)N═C(NH2)—O—C1-C2-alkyl;
• or is
• (iv) a group —CH(R3)—N(R4)—C(O)-T1, wherein R3 is H, C1-C6-alkyl, C1-C6-haloalkyl, halogen or cyano, R4 is H;
• C1-C4-alkyl, C2-C4-alkylcarbonyl or C2-C4-alkoxycarbonyl, and T1 is independently defined as T above;
• (b) a radical of formula
• wherein R5′ is H, C1-C2-alkyl, C1-C2-haloalkyl, halogen, nitro or cyano, and Q is as defined above;
• (c) a radical of formula
• wherein Q′ is a radical as defined in embodiments (ii), (iii) and (iv) for Q above;
• or
• (d) a radical of formula
• wherein n is 1 or 2 and Q″ is a group —N(R4)—C(O)-T2, wherein T2 independently has the meaning of T above and R4 is as defined above;
• for controlling sea lice on fish.