METABOLISM DURING DELAYED HATCHING IN TERRESTRIAL EGGS OF A MARINE FISH, THE GRUNION LEURESTHES TENUIS

California grunion, Leuresthes tenuis (Osteichthyes: Atherinidae), lea ve the ocean to spawn in the sand following extreme high tides in summ er. Eggs develop out of water and are able to hatch within 9-13 d, the primary hatching period. Eggs hatch on immersion and agitation by wav es at the next extreme high-tide series. However, if the waves do not reach them and hatching is not induced, eggs remain viable In the sand for several weeks. During this period, grunion eggs will delay hatchi ng but will hatch at any time if immersed and agitated in seawater. Eg g metabolism during embryonic development was measured by aerial respi rometry. Metabolism increased linearly until the first date at which e ggs were;able to hatch. At that time, metabolic rate stabilized and re mained constant for two additional weeks of embryonic incubation. Larv ae induced to hatch after different durations of incubation within thi s period were not significantly different in length; however, the amou nt of oil contained in the yolk decreased linearly during the delayed hatching period. Mie suggest that the increase in grunion egg metaboli sm during the time to primary hatching capability, and the steady, hig h metabolic rate throughout the delayed hatching period, permit reprod uction in the unique niche of these marine eggs. These semiterrestrial anamniotic eggs develop quickly and remain continuously ready to hatc h over an extended period in response to an environmentally dependent and somewhat unpredictable embryonic timetable.