Since the ‘90s, the Dutch label Konkurrent has been inviting pairs of bands to collaborate for its In the Fishtank series, providing groups with two days of studio time to record material for release. (Some Fishtank albums only feature a single band and one album finds three outfits working together.) In the Fishtank 15 features the intriguing combination of Austrian electronic musician Christian Fennesz and the American singer/songwriter Mark Linkous, who releases music under the name Sparklehorse. The result is a loose, atmospheric work dominated by two lengthy instrumentals, “Music Box of Snakes” and “NC Bongo Buddy.” On the former track, manipulated music-box tones, spare piano, cello, and electronic sounds conjure a haunted strip of abandoned shoreline. Despite the title, “Bongo Buddy,” is free of drum patterns or driving rhythms; instead, hazy textures, stray guitar tones, and other elements color this dreamy and dramatic cut. “Goodnight Sweetheart,” which features singing that sounds as if it’s gurgling up from the Great Deep, is one of two cuts that hint at song form. The other, “If My Heart,” is a nice piece of psych centered around Linkous’s touching vocals.