Osisko Development (ODV) had the highest return in April 2016 by a small-cap US stock, returning 700%.

ASSET	MONTH	% RETURN
Osisko Development (ODV)	April 2016	699.99%
Metalla Royalty & Streaming (MTA)	April 2016	499.83%
Byrna Technologies (BYRN)	April 2016	440%
TSS, Inc Common Stock (TSSI)	April 2016	185.31%
Dolly Varden Silver (DVS)	April 2016	140.51%
International Tower Hill Mines (THM)	April 2016	136.8%
GoldMining (GLDG)	April 2016	119.72%
SIGA Technologies (SIGA)	April 2016	100.03%
Global Ship Lease (GSL)	April 2016	97.42%
NGL Energy Partners (NGL)	April 2016	78.93%
Natural Resource Partners (NRP)	April 2016	77.79%
Americas Silver (USAS)	April 2016	72.55%
Silvercorp Metals (SVM)	April 2016	71.94%
eXp World (EXPI)	April 2016	70.92%
Mesabi Trust (MSB)	April 2016	69.26%
Genco Shipping & Trading (GNK)	April 2016	68.85%
EZCORP (EZPW)	April 2016	67.8%
POET Technologies (POET)	April 2016	67.16%
Euroseas (ESEA)	April 2016	66.13%
Valhi (VHI)	April 2016	64.17%
Helix Energy Solutions (HLX)	April 2016	60.41%
Ryerson (RYI)	April 2016	60%
Vital Energy (VTLE)	April 2016	59.84%
CorMedix (CRMD)	April 2016	59.54%
Galiano Gold (GAU)	April 2016	54.76%

Small-cap stocks are treated as having a market cap between $300M and $2B.