In principle yes. But that ignores that the GDR built those cars to use, and has no need for the fish. Nor had it any say in whether to do the trade. The USSR messed up their own planning so they pressured the GDR. Inside the GDR it was a meme that you bought a car for your kid no later than when it got born so it’d get delivered on the 18th birthday but frankly speaking the GDR did produce a fuckton of cars – but couldn’t keep them. Which is why they stopped investing into developing the thing which is how you ended up with the same Trabants being built in 1990 as in 1958.
Other trades were more equitable, including the steady stream of raw materials coming in from the USSR in exchange for industrial machinery. The GDR also traded a fuckton with the west, more or less washing machines, fridges, textiles and industrial machinery, against the Prussian necessity: Coffee. Until they kick-started the Vietnamese coffee industry to be able to afford bananas better but that investment didn’t pan out because 1990 came along, coffee plants take something like 10 years to start bearing fruit. The Vietnamese produce excellent coffee, btw.
Main point though is that yes the USSR was treating all the other bloc states as vassals: If they wanted to do a trade, they got it, no matter how insanely lop-sided it was.