Watch the program called “River Monsters” on bull sharks, they provided significant evidence that they can breed in fresh water as well.
In Australia there is a river which is blocked by a relatively low dam. Back in the 80’s (I believe) it went underwater from massive floods. Well now there are bull sharks both large and small living above the dam. The small sharks pretty much had to have been born in fresh water.
Peter Capstick in “Man Eaters” wrote of a similar situation in Central America.
From wiki: “.Bull sharks have occasionally been seen in the Mississippi River as far north as St. Louis[10]. Even more rare, due to cooler waters, bull sharks have made their way up the Illinois River and into Lake Michigan such as an encounter off the coast of Chicago, Illinois[11]. In that incident the shark was verified by U. of Illinois biologists as being a female 6 feet 9 inches and weighing over 300 lbs.”
WOW!