Aria does not approve of this picture.  
She thinks that it is fishy.

Meanwhile, Sonata was in the middle of a tacos binge.

She’s like hah! Got yah XD

Don’t be so grumpy, Aria. This is just her way of saying “I love you.”

An odd way to go fishing.

“After I pinch your ears some more I will give you lots of snuggles.”

@Mrmildock  
Sounds about right for their dynamic. :)
 
Adagio: “Wooz my cute widdle fishie-wishie? Who haz doze soft widdle squishy ears?”
 
Aria: “_Urrrrgh…”
 
During such times, Sonata sits somewhere out of sight, just happy it’s not her this time.

Adagio being the big fish she is(no pun intended) decides to prove her dominance by humiliating her sisters. Sonata being more cowardly allows Adagio to boss her around. Aria tends to put up a fight, but then this happens. And Dagi isn’t even trying folks, which adds more salt to the wounds for poor Aria.

Adagio Dazzle: “Ah, Aria-chan, Your Pony ears are a-so kawaii. Have a-me pinch them for you.”  
Aria Blaze: “Omae ga saiaku…”