 Several theories have been proposed as to why this specific subject – not a very common theme in art history – was chosen . One suggestion sees the painting as a justification for the so @-@ called catasto of 1427 ; a new form of income tax . This is not a very likely explanation , however , as Brancacci would stand to lose from the new taxation , and would probably rather have been among its opponents . A more probable explanation links the painting to Pope Martin V 's 1423 agreement that the Florentine church be subjected to state tax . The money found in the fish 's mouth can also be seen as an expression of how Florence 's wealth came from the sea . Felice Brancacci , a silk merchant involved in Mediterranean trade , was also a member of the city 's Board of Maritime Consuls . 
