Eggs and larvae of Awaous melanocephalus (Teleostei: Gobiidae)

Abstract

The morphology of eggs and larvae of Awaous melanocephalus is described. The eggs measured 0.33-0.35 mm in long-axis diameter and 0.32-0.34 mm in short-axis diameter. Newly hatched larvae (0.90-0.99 mm in notochord length, NL; 0.93-1.04 mm in total length, TL) were poorly developed, lacking a mouth and having a large yolk sac and unpigmented eyes. The mouth opened and the eyes became fully pigmented 3 days after hatching (1.78-2.00 mm NL, 1.88-2.10 mm TL). The yolk sac was completely absorbed 5 days after hatching at a water temperature of 27º-28ºC.Key words Egg · Larva · Amphidromous goby · Awaous · Gobiidae length (TL), and yolk-sac diameter were measured using a micrometer after fi xation in 5% formalin solution. The sketched specimens were preserved in 70% ethanol and deposited in the collection of the University of the Ryukyus, Marine Science (URM). Results and DiscussionSixteen discrete nests were found in the Genka Stream from July to October 2005. Water temperature at the time nests were discovered ranged from 24.7º to 29.5ºC. Eggs being guarded by males (70-130 mm SL, n = 16) were attached to the surface of one or more stone(s) or rock(s) in a single layer by adhesive fi laments. The total area of egg masses in a single clutch ranged between 40 and 220 cm 2 . All the eggs in a nest appeared uniform in texture and color, suggesting that each nest consisted of a single clutch, and estimated to contain about 40 000-220 000 eggs (mean ± SD = 102 000 ± 54 000, n = 16). A positive relationship was observed between the SL of the guarding male and clutch size ( Fig. 1; r = 0.51, P < 0.05, n = 16). Eggs ranged between 0.33 and 0.35 mm (mean ± SD = 0.34 ± 0.01 mm, n = 10) in long-axis diameter and 0.32 to 0.34 mm (0.32 ± 0.01 mm, n = 10) in short-axis diameter ( Fig. 2A), and embryos hatched within 6 h after collection.Mean egg size in Awaous melanocephalus was similar to that reported for Hypseleotris compressa (0.30-0.32 mm in long-axis diameter; Auty, 1978), which are thought to be among the smallest known eggs in teleosts (Miller, 1984). The fi nding that A. melanocephalus spawns small eggs corroborates similar fi ndings in the conspecifi c Awaous guamensis (see Ha and Kinzie, 1996). However, A. melanocephalus differed from A. guamensis with respect to the guarding of egg masses. While the female is primarily re- IchthyologicalResearch

Early hatch: a strategy for safe downstream larval transport in amphidromous gobies

“…Yamasaki and Tachihara (2006) found that in Stiphodon percnopterygionus from Okinawa, the larvae hatch only 20 h after fertilisation, and are 1.26-1.35 mm long. Also, Yamasaki and Tachihara (2007) found that larvae of Awaous melanocephalus were 0.93-1.04 mm long at hatch. Miller (1984) told of minimal bestowal (provision of energy resources) in diadromous fluvial gobiids that hatch within only seven hours of fertilization, and whose tiny larvae are swept downstream to the sea; he considered that some gobiids (which he described as ''anadromous'' but they are actually amphidromous) hatch at less than 1.5 mm, the larvae of Dormitator latifrons being merely 0.8-0.9 mm long.…”

Life histories of closely related amphidromous and non‐migratory fish species: a trade‐off between egg size and fecundity

“…This particular trait appears to have evolved independently a number of times in the three orders of amphidromous fish that have given rise to significant freshwater radiations, that is, Osmeriformes, Perciformes and Scorpaeniformes. For example, the amphidromous goby Awaous melanocephalus (130 mm SL) produces very small eggs (0.33-0.35 mm long and larvae 0.93-1.04 mm total length, amongst the smallest known eggs and larvae of any teleost; Yamasaki & Tachihara, 2007). Our conservative data set underestimates the frequency that larger eggs have evolved in association with a non-migratory life history, given that other non-migratory species of Galaxias, Rhinogobius, Cottus and Micropercops (Odontobutidae), for Table 2. which closely related amphidromous ancestors could not be identified, also have relatively large eggs compared with amphidromous species in the same or closely related genera (McDowall, 1970(McDowall, , 2010bPatten, 1971;Humphries, 1989;Goto, 1990;Iwata et al, 2001).…”

“…Phylogenetic analyses suggest the trait has evolved at least five times within the genera Galaxias, at least once in Neochanna, twice in Gobiomorphus, and at least twice (but potentially several times) in Cottus and Rhinogobius. For a relatively small fish (130 mm), their fecundity is impressive producing up to 220 000 eggs per clutch (Yamasaki & Tachihara, 2007). Small eggs, small larvae and high fecundity are characteristic of many amphidromous fish species, particularly amongst the diverse range of gobioid fish that exploit this particular life-history strategy (Keith, 2003;Murphy & Cowan, 2007;Iida, Watanabe & Tsukamoto, 2009;Yamasaki et al, 2011).…”

Performance and scaling of a novel locomotor structure: adhesive capacity of climbing gobiid fishes

“…Many species living in the streams of oceanic islands exhibit an amphidromous life history, in which larvae are swept downstream to the ocean upon hatching (e.g. Maciolek, 1977;Radtke et al, 1988;Fitzsimons and Nishimoto, 1995;Yamasaki and Tachihara, 2007;Maeda et al, 2008;McDowall, 2009). After growing for several months, postlarvae return into stream habitats where they undergo metamorphosis and grow to reproductive individuals (Radtke et al, 1988;Bell, 1994;Shen et al, 1998;Radtke et al, 2001).…”