How to amplify a low Amplitude, High frequency signal from Ultrasonic Transducer?
You need an amplifier  that has a high enough gain-bandwidth product, definitely above a few MHz, preferably 10-20MHz for a reasonably stable gain, assuming a sine wave at 125kHz. If your signal has a lot of higher harmonics, then higher. Using too high performance an amplifier will incur a power penalty without giving you much benefit. 

The slew rate is not too important, given your low 100mV output, but in any case it needs to be higher than \$2\pi f V\$ so about 0.1V/\$\mu\$sec. 

Multiple amplifiers are often used to get high gain at wide bandwidth, since you can get a gain of 1000 with two or three amplifiers of gain 31.6 or 10 rather than trying to find an amplifier with a gain-bandwidth product in the GHz range, which will surely run quite hot and will probably be tetchy and oscillate if you look at it crosswise. 

If you are really looking for micropower you may do better with a discrete transistor design than with a general purpose op-amp.