• Hot Stove Tracker
Among the prospects left exposed are Reymin Guduan (ranked 16th by MLB.com in the club's Top 30), outfielder Teoscar Hernandez (17th), right-hander Chris Devenski (18th), outfielder Danry Vasquez (20th), right-hander Brady Rodgers (22nd) and right-hander Kyle Smith (29th).
• Top 30 Prospects
Players first signed at age 18 must be added to 40-man rosters within five seasons or they become eligible to be drafted by other organizations through the Rule 5 process. Players signed at 19 years or older have to be protected within four seasons. Clubs pay $50,000 to select a player in the Major League phase of the Rule 5 Draft, slated to take place on Dec. 10. If that player doesn't stay on the 25-man roster for the full season, he must be offered back to his former team for $25,000.
Gonzalez, 23, hit .321 with six doubles, two home runs, 35 RBIs and a .409 on-base percentage in 72 games across three levels last season, finishing at Double-A Corpus Christi. He threw out 24 of 51 runners attempting to steal.
The hard-throwing Gustave, 23, went 5-2 with a 2.15 ERA and 20 saves at Corpus Christi en route to being named a Texas League Midseason All-Star. He also led all Astros Minor Leaguers in saves, converting 20 of 24 opportunities. Gustave -- No. 28 in the organization -- was selected in last year's Rule 5 Draft by Boston, only to be returned to the Astros in April.
Minaya, 25, combined to go 1-0 with a 2.80 ERA in 35 relief appearances with Triple-A Fresno and Corpus Christi in 2015. He recorded 59 strikeouts in his 54 2/3 innings and allowed just two home runs.
Musgrove, 22, -- ranked No. 9 in the organization -- was the Astros' 2015 Minor League Pitcher of the Year after combining to go 12-1 with a 1.88 ERA, 99 strikeouts and eight walks between Corpus Christi, Class A Advanced Lancaster and Class A Quad Cities.
The 6-foot-7 Paulino, 21, went 5-3 with a save and a 2.81 ERA in 13 games (12 starts) across three levels of Class A ball. The club's No. 19 prospect, Paulino struck out 72 hitters in his 67 1/3 innings pitched, allowed a .200 opponents' average and a 1.01 WHIP.
Aplin, 24, played in 105 games between Fresno and Corpus Christi, batting .296 with 32 stolen bases and a .413 on-base percentage.
Fontana, 24, played in 117 games at Fresno, making 52 starts at shortstop, 30 starts at second base and 23 starts at third base while posting a .369 on-base percentage and 21 doubles.