Integra Resources (ITRG) had the highest return in April 2019 by a small-cap US stock, returning 400%.

ASSET	MONTH	% RETURN
Integra Resources (ITRG)	April 2019	400%
Red Cat (RCAT)	April 2019	300%
Nutex Health (NUTX)	April 2019	160%
Jumia Technologies (JMIA)	April 2019	126.75%
Lightbridge (LTBR)	April 2019	71.37%
Adient (ADNT)	April 2019	69.48%
Aspen Aerogels (ASPN)	April 2019	61.02%
Ocugen (OCGN)	April 2019	60.42%
Alphatec (ATEC)	April 2019	57.99%
Opera (OPRA)	April 2019	47.18%
Savara (SVRA)	April 2019	43.94%
FinVolution (FINV)	April 2019	40.29%
Arvinas (ARVN)	April 2019	40.07%
Ridgepost Capital (RPC)	April 2019	38.95%
Hovnanian Enterprises (HOV)	April 2019	38.36%
High Templar Tech Limited Sponsored ADR Class A (HTT)	April 2019	36.43%
Cantaloupe (CTLP)	April 2019	35.65%
Syndax Pharmaceuticals (SNDX)	April 2019	34.4%
Genco Shipping & Trading (GNK)	April 2019	33.78%
Power Solutions International, Inc Common Stock (PSIX)	April 2019	32.87%
Achieve Life Sciences (ACHV)	April 2019	30.77%
Meta Financial (CASH)	April 2019	29.64%
Pagerduty (PD)	April 2019	27.62%
LSI Industries (LYTS)	April 2019	27.34%
DBV Technologies (DBVT)	April 2019	27.28%

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