First Record of Butis humeralis (Gobiiformes: Butidae) from the West Coast of India with special emphasis to its Early Developmental Stages

Dark sleeper or olive flathead-gudgeon, Butis humeralis (Valenciennes 1837), was discovered for the first time from the west coast of India. Till date, there have only been reports of this species from India's east coast. A cluster of sparsely distributed eggs of B. humeralis were observed in the gritted glass panel submerged for biofouling studies in aquaculture cage sites near Kalamukku fishing harbour in the Cochin Estuary. The egg mass covered an area of 61.80 cm ² with an average abundance of 124.51 ± 27.25 eggs/cm ² . Molecular characterization of the eggs was done to affirm the species identification. The eggs of B. humeralis were, adhesive, pyriform-shaped and translucent with brownish yellow colour with a size measurement of 0.41 ± 0.01 mm and 0.36 ± 0.01 mm diameters along long and short axis, respectively. The eggs were reared up to 144 hph (hour post-hatch) subsequently. The newly hatched larvae of B. humeralis were slender and translucent with 1.01 ± 0.037 mm total length (TL) with a yolk sac of size 0.624 ± 0.05 mm and 0.415 ± 0.05 mm along longitudinal and horizontal axis, respectively. After 72 hph, fully pigmented eyes were observed whereas a well-developed mouth with distinct upper and lower jaw appeared on the fifth day of hatching. The TL of the preflexion larvae after 144 hph ranged between 2.08–2.12 mm. The first report of this lesser-known species from the west coast of India demonstrating the developmental stages signifies the need to evaluate their current ecological and conservation status in the ecosystem.