Recruitment

Bell main site page || main goby page --- How it started -- Intro -- Larvae -- recruitment

See also the paper "Overview of Goby-Fry Fisheries"

The fish (all recruiting fish species) are commonly called tritri or twitwi or titiwi or titiri in Dominica. This may be a Carib or possibly Arawak word. It was reported by Atwood in 1791 as 'trez-trez'. In Puerto Rico they are called seti (and there is an annual seti festival). In Jamaica the word 'ticky-ticky' probably applies to these also (but perhaps applies to any small fish) -- it has some similarity of sound to 'titiwi'. In the Philippines they are called ipon or hipon (meaning seems to have shifted since the time Manacop (1953) described the words; some use both for shrimps (recruit at the same time).

<--Recruiting gobies in a fast section of a rocky stream (just below the culvert bridge at stn PHW, the PH Williams Co. sand/cement works on the Canefield River, Dominica 891217).

They are inching their way along the splash zone. This probably saves them energy, and they probably wouldn't do this if there were herons etc. about, because they hop back into the water if you move too close. They can, however, swim in this current if they have to: I tried holding a net in the current to the left, and scaring a lot of them to jump into the water, then lifting the net. I expected to get most of them, but I got none of them. It is possible that such burst swimming is only sustainable for a very short time. They can also inch their way, while in contact with a surface, against very strong currents, such as creeping into the outlet of a pump.

<-- FISHERY: the "till"* fishery at Layou for postlarvae (locally called tri-tri) of Sicydium punctatum and other anadromous gobies. Tri-tri appear in rivers each lunar month, on the 4th day following the last lunar quarter.

(*The "till" is a fine meshed net, or beach seine, and walked (it has loops at each corner) through shallow water, usually just outside the river mouth. Important to note the area is sandy, and fish are likely benthic in other areas with solid substrate (or grain sizes bigger than sucker diameter).)

The postlarvae return to river mouths on the FOURTH DAY after the LAST LUNAR QUARTER. Very precise. (Timing varies worldwide.) And they aren't alone: for company they have another Sicydium antillarum, Eleotris pisonis, ?Awaous taiasica, a few rarer gobies, PLUS several species of shrimps and one or two Neritid gastropods. Anadromous snails, yet. All recruiting with the same lunar phasing. (See life cycle)

Other fish also appear with the recruitment migration; some are predators attracted by the gobies and shrimps. Some we aren't sure about.

<--FISHERY: subsistence method, 'bag-and-stones'. A mesh bag (e.g. feed or fertiliser bag) is ripped partly open, filled with stones, and placed in the stream with the open end facing downstream. Postlarvae make their way through the stones and are stopped by the mesh. Atwood (1791) reported a similar method, using baskets. I consider it likely that this is an adaptation of a precolumbian method.

Recruits = postlarvae that have returned to fresh water. Newest recruits are transparent (no pigment pattern at all) and have few scales. Scalation begins at caudal peduncle.

From top, identification and abundance as percentage of typical fish catch* (all species recruit at the same lunar phase [*excluding crustacea]):
4 Sicydium punctatum (>95%), ~20mm
1 Sicydium antillarum (~2-5%) ~25mm
1 Eleotris pisonis (<1%) ~12mm
2 Gobiesocidae (unidentified) (<<1%) ~10mm
Neritidae (gastropoda) are not caught in the 'till' (beach seine) gear as used at Layou River mouth, but are caught in traps (bag-and-stones, subsistence fishery) or my upmigration traps. Here (below, with rulers) are some that died during shipping, after having lived in captivity 1991-1996, collected at not much smaller size (at Canefield), though Neritids are frequently seen over 20mm in Dominica (it could be there are 2 species, or one very slow-growing one). They produced enormous numbers of veligers during that 5 years, and tended to be gregarious in the aquarium; they were never far from each other.

not shown:
Awaous taiasica (identified according to Brockmann 1965; this identification questioned by Helen K. Larson) (~0%)
Decapod crustaceans (shrimps of families Atyidae and Palaemonida) are caught in the 'till' gear, but discarded (often somewhat spitefully, by dumping above the water mark, as if they were considered a pest) although they have excellent flavour (but spiky texture).