sargassumfish reproduction

8/10/2019 Sargassumfish Reproduction

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Information on Aquarium Culturing of Saltwater Fishes and Invertebrates

Report on the spawning of Sargassum fish,H i stri o histri o Article by Binu Varghese, Ph.D., Trivandrum, Kerala, India. Copyright 2006.

Photos by the author

The fishes were collected from thefloating/drifting sargassum weeds off Vizhinjamcoast (South west coast of India, Near KovalamBeach) to the marine aquaria and ResearchCentre of Central Marine Fisheries ResearchInstitute, Vizhinjam. Fishes (6-8) were kept in 5ton circular FRP quarantine tanks for theirforward transition to the exhibit tanks. Two ofthe fishes were observed to have highly inflatedabdomens. The second evening between 1600 -1630 hrs there was a splashing sound in thequarantine tank and upon inspection atransparent gelatinous object was found. It was found floating on the water surface (see

photographs below). The egg mass/raft appeared to be double layered with slightly larger middleregion and blunt ends at both sides. The length of the egg mass/raft was found to be about 30-35cm. The egg mass/raft was transferred to a 500 L tank in a flow though system after an hour.

Moderate aeration was given initially as the air bubbles started attachingto the gelatinous membranes. The airstone was removed and only slight

bubbling near the surface was allowed to give water movement. By thesecond evening, the gelatinous matrix began to disintegrate. Microscopicanalysis of the eggs found them to be undivided/unfertilized anddecaying.

Folded egg mass/raft in beaker:

The next week, another spawning was observed in exactly the same manner. This time the eggmass/raft was taken for photographs after giving sufficient time for fertilization (if any). Again,unfortunately, no embryo development was observed.

Size female (mm): 100-120Food given: Live mysids, small fishes, boiled mussel meatTank: Fishes were kept in 5000 liter FRP quarantine tanks


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Spawning

Unfortunately, I couldnt observe any courtship behaviour or pre -spawning activity. The shearsize of the egg mass/raft indicates the need of external pressure to release the massive egg mass.The females were observed in a mature condition along with a group attached to driftingsargassum weeds. The females had round abdomens, apparently in a bursting condition. Thefemale made a splashing sound while releasing the egg mass. In both cases, the egg mass/rafts

were found attached to the air tubes just where it touched the water surface. Its definitely a promising species for reproductive biology studies.

Spawning occurred in the open water column near the surface. The splashing sound heardindicates the release occurred very close to the surface. In both cases the females released theeggs near the surface and the egg masses were found laid over the airline floating on the watersurface. This may be a spawning behaviour in this species as in nature the fishes were foundamong the floating sargassum weeds. This behaviour might be an adaptation for ensuring properfertilization in this species as their entire habitat is highly mobile.

There is every possibility that fertilization is external. As in both the cases the eggs were found

unfertilized and no cell division was noticed. Its also very unlikely to have internal fertilizationin this species as the ova are well protected inside the gelatinous matrix.

There are two possible points where fertilization could occur:

(1) when the ova are still in the matrix and the sperm find their way into it. This is like that oftheir family members like lion/scorpion (Pterois) where the egg balls are formed, the malefertilizes them and his sperm enters into this matrix. In this case, the lack of egg developmentmay be due to the absence of males/mature males in the group.

Microphotograph of Eggs/Ova:

(2) Another probability is that fertilization occurs after the dissolution of the gelatinous structure.If the fertilization occurs at this time, then timing has to be very essential. In the open ocean, the

chances of fertilization are limited if the egg mass is moving as sargassum fishes tend to be slowmovers and rarely find it comfortable to move away from the weeds. This also explains the behaviour of surface spawning and the necessity to attach/hang the egg masses on floatingobjects. The morphology and mobility of the sperm of the species will be of great interest.

Egg mass/raft description Large (30-35 cm), gelatinous, transparent, apparently double layered structure with numerouseggs egg/ova embedded in the matrix spaces (see photos). The middle portion of the egg


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mass/structure was distinctly wider than both ends, though the ends were not tapering (something like elliptical with blunt ends). I was unable to locate any exterior opening of the egg mass,

perhaps because I took too much care not to spoil the eggs.

Egg development No development was noticed; the matrix disappeared on the second day. This provided greatspace for the microbes to develop and the eggs were decayed.

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sargassumfish reproduction

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