Variations of sperm release in three batches of zebrafish

Abstract

By collecting and counting the number of sperm released during separate matings in three batches of zebrafish Danio rerio, aged 3-4, 4-5 and 5-6 months, males were observed to release sperm before the female started laying their eggs. After the female left the nest, the number and motility of sperm and life span of sperm of younger fish were higher than those of older fish in water samples collected under the nest and at the surface of the tank. Sperm were released in the form of sperm trails laid on the nest surface, subsequently active spermatozoa left the trails and moved in the water for several minutes. Sperm trails consisted of bands of viscous material in which the sperm were embedded. In most cases eggs were not laid directly over the sperm trail, suggesting that sperm may contact the eggs after the latter are released into the water. In all the three tested groups there was no significant difference (P > 0Á05) between the number of sperm collected on some portions of the acetate sheets which lined the nest ceiling. This result demonstrated that the greater activity of younger fish accelerated the sperm dispersal in water. Male sperm duct glands, seminal vesicles, known to secrete mucosubstances are probably involved in the production of sperm trails. The possible influence of insemination on the mating style of zebrafish is discussed. # 2004 The Fisheries Society of the British Isles

Comments on ‘Variations of sperm release in three batches of zebra fish’

“…Males have a slim compressed body form with an inconspicuous genital papilla, whereas females display a distinct genital papilla and a deeper body form (Laale, 1977). This contrasts with the observations of Kemadjou Njiwa et al . (2004) who state that males possess an elongate genital papilla that they use to deposit sperm onto a nest surface.…”

“…12 eggs during each oviposition event. Again, this differs from the observations of Kemadjou Njiwa et al . (2004), who observed pairs releasing gametes asynchronously in a nest site with females laying eggs one at a time.…”

“…In a recent paper, Kemadjou Njiwa et al . (2004) discussed details of the spawning behaviour of what they refer to as the ‘zebra fish Danio rerio (Hamilton)’.…”

“…Another feature common to male gobioids is the presence of sperm‐duct glands (or ‘seminal vesicles’) associated with the testes (Miller, 1984). Kemadjou Njiwa et al . (2004) hypothesize that such glands in the zebra fish may produce the adhesive material they described in the sperm trails of this species.…”

The Effect of a Depth Gradient on the Mating Behavior, Oviposition Site Preference, and Embryo Production in the Zebrafish, Danio rerio

“…Previous studies of zebrafish in a lab setting described basic mating behaviors, including elliptical movements made by the male around the female and the subsequent oviposition of 5–20 unfertilized eggs, which are then fertilized by released sperm (Guthrie, 1993; Darrow and Harris, 2004; KemajouNjiwa et al ., 2004). Observation of the zebrafish in their natural environments suggests that they prefer to mate along the shallow shorelines (Rowena Spence, personal observation).…”