Field Report on Gobies Commonwealth of Dominica June 2006 Jason Zapalac
Abstract
This is a field report on Gobies in the Commonwealth of Dominica. It identifies diagnostic characteristics, behavioral characteristics, habitats, identification and presents observations of territory and territorial behavior of the species. This report may serve as a guide to the behavior of gobies in the Checkhall River, Commonwealth of Dominica.
Introduction
There are currently 212 genera and 1,875 species of gobies identified, making gobies the largest marine fish family. Gobies on average never exceed 10 cm, making them among the smallest know vertebrates (Murdy 2004). On volcanic islands, gobies are the most common freshwater fish that can be found. However due to their color and behavioral characteristics they are the least recognized. All goby species on Dominica are native to the island. They are found in freshwater, saltwater and brackish waters and are abundant in rivers of coastal volcanic topography (Fishbase). Gobies fall into the following classification: • • • • • • Kingdom: Animal Phylum: Chordata Class: Actinopterygii Order: Perciformes Family: Gobiidae Sicydium punctatum o Tritri (common name) is the most commonly found species of gobies on Dominica. o Awaous banana (no common name) is another species of goby found in Dominica.
(www.fishbase.org)
Behavior
Gobies have an excellent ability to exploit their environment. They use areas that other fish and aquatic species are unable to use. Gobies use the cracks and crevices formed by the rocky bottom to protect themselves from predators. Observation will show that they will not travel far from a safe place to hide, and at the moment of threat will retreat to those protected areas. Observation of the gobies showed many characteristics. 1. They are sensitive to movement and light. a. Upon sensing danger they would hide in a protected area for no more than five minutes. 2. They swim from rock to rock randomly. 3. They are territorial. a. You can find the same goby in the same area anytime. b. They may chase other gobies away, but leave other aquatic organisms alone. c. Sometimes they will let other gobies in their area.
Habitats
Goby species can be found in all types of fresh, salt and brackish water and each species can vary, in its preferred habitat. Some species will migrate between fresh and saltwater and back to freshwater to complete a life cycle. They can usually be found in mud and rubble where they are safe and naturally blend into its surrounding environment. Some species (Ambyeleotris and Cryptocentrus) will share a burrow with a snapping shrimp (Alpheus), forming a symbiotic relationship. Goby eggs are usually guarded and tended by males and the massive amounts of eggs are laid by the females (Murdy 2004).
Diagnostic Characteristics
There are several characteristics that define gobies. These characteristics are: • • • • Size: > 10cm Fins: majority have united pelvic fins forming a ventral disc Body: stout Head: short and broad
• • • •
Snout: rounded Teeth: small, sharp and conical and are one to several rows Gill membranes: broadly joined to isthmus Color: variable
There are also no lateral lines on the body (Murdy 2004).
Identification
Identification characteristics of the three gobies found on Dominica. Sicydiinae • • Dorsal and anal fins separated from caudal fin (1). Both dorsal fins typically separate (2). (2) (1)
•
Lower jaw typically possessing only a single row of teeth (3) (Murdy 2004). (3)
Awaous • • • • Two dorsal fins; eyes larger, 15% or more of head length; body robust or elongate; maximum size of adults to 30 cm. No crest present on nape. Body completely scaled; vomer without teeth. Shoulder girdle, under gill cover, with distinct fleshy lobes.
•
Longitudinal scale rows typically more than 60, often more than 70; first dorsal fin yellowish green (Murdy 2002)
Observations of Gobies in the Checkhall River
Materials and Methods • • • Pen and paper Tape Measure Clock with secondhand
The best time to observe gobies in the Checkhall River is noon to mid-afternoon, when the sun is directly overhead and there is plenty of light to see in the water. Caution must be taken to not scare the gobies away, so you can observe them in their usual territory. If they are disturbed they will return within about 5 minutes. There are different pools of water located along the river. Each pool has a chance of a goby inhabiting the pool. Once a pool was found with a goby inhabiting it, behavior observations were made. Time recording Observation of the gobies will show that they will swim from rock to rock in their territory and stay for a certain amount of time. This time can be measured and recorded to find an average of time they stay in one place. Mapping Their territory should be mapped out and measured to find a total area in square feet. Depth is not considered as a territory parameter because the gobies are bottom dwellers. The area measurements should be made after the observations so the goby’s behavior is not affected. This method can be replicated any day, observing the same individual goby. Inter-territorial behavior Other territorial gobies can also be identified, as well as the social behavior between the territorial individual and the invader. The behavior of the individual towards each other is observed and noted. Whenever one goby comes in contact with another, during observation time, their reaction was noted.
Observations Pool #1 Jun-04-2006 Key map features: A: Submerged Maroon Rock B: Submerged Orange Rock C: Submerged Orange Rock : Direction of flow &: Rock above water •, ▪, x : where goby landed on rock (in plot 1, 2, 3 respectfully, marked territory) Using the second hand on a clock, five landings were recorded and averaged to determine how much time the gobies stayed on a rock. The results are as follows:
Plot 1 :11 - :13 :21 - 1:35 :41 - :33 :45 - :53 :02 - :47 Average: 2 sec 74 sec 52 sec 8 sec 45 sec 36.2 Plot 2 :19 - :54 :56 - :07 :11 - 1:17 :21 - :35 :42 - :04 35 sec 11 sec 126 sec 14 sec 22 sec 41.6 Plot 3 :47 - 1:02 :06 - :34 :39 - :44 :42 - :11 :16 - :23 80 sec 28 sec 5 sec 29 sec 7 sec 29.2
Total Plot Areas Plot# 1 2 3 Length x Width 1.25m x 1.16m 1.4m x 1.25m 1.34m x 1.01m Total Area 1.46m2 1.75m2 1.35m2
Inter-territorial behavior Reaction Plot 1 Plot 1 Plot 2 Plot 3 x o Plot 2 x o Plot 3 o o X: attacked O: ignored
Observation notes • • When the gobies in plot 1 and 2 interacted, the goby in plot 1 chased away the goby in plot 2. The gobies in plots 2 and 3 never interacted with each other upon invasion into the others territory.
Pool # 2 Jun-04-2006 Key map features: A: Submerged Orange Rock B: Submerged Tan Rock C: Submerged Maroon Rock D: Submerged Maroon Rock : Direction of Flow &: Rock above water •, ▪, x : where goby landed on rock (in plot 1, 2, 3 respectfully, marked territory)
Using the second hand on a clock, five landings were recorded, for each of the three gobies occupying neighboring areas, and their time averaged to determine how much time the gobies stayed on a rock. The results are as follows:
Plot 1 :05-:32 :58-1:33 :35 - 2:30 :40 - :53 :10 - :37 Average: 27 sec 95 sec 175 sec 13 sec 27 sec 67.4 sec Plot 2 :03 - 1:42 :50 - :58 :01 - :23 :30 - 1:02 :10 - :36 159 sec 8 sec 22 sec 92 sec 26 sec 61.4 sec Plot 3 :32 - :45 :53 - 1:24 :30 - :57 :00 - :36 :38 - :59 13 sec 91 sec 27 sec 36 sec 21 sec 35.6 sec
Total Plot Areas Plot # 1 2 3 Length x Width 1.71m x .73m 1.04m x .88m .88m x .52m Total Area 1.25m2 .92m2 .46m2
Inter-territorial behavior Reaction Plot 1 Plot 1 Plot 2 Plot 3 o o Plot 2 o o Plot 3 o o x: attacked o: ignored
Observation notes • There was no inter-territorial aggression between any three plots in pool 2
Pool # 3 Jun-04-2006 Key map features: A: Submerged Maroon Rock B: Submerged Maroon Rock C : Submerged Maroon Rock : Direction of Flow & : Rock above water • : where goby landed on rock
Using the second hand on a clock, five landings were recorded below: Plot 1 :05-:15 :23-:42 :51-:03 :10-1:23 :32-:05 Average 10sec 19sec 12sec 73sec 33sec 29.4 seconds
Total Plot Area Plot # 1 Length x Width 1.07m x .91m Total Area .97m2
Inter-territorial behavior None, because no other gobies occupied pool #3.
Pool # 4 Jun-04-2006
Key map features: A: Submerged Maroon Rock B: Submerged Maroon Rock C: Submerged Maroon Rock D: Submerged Maroon Rock E: Submerged Maroon Rock F: Submerged Maroon Rock : Direction of Flow &: Rock above water • : where goby landed on rock
Using the second hand on a clock, five landings were recorded below: Plot 1 :37-1:23 :49-:17 :29-:54 :02-:19 :23-:32 Average 106sec 28sec 25sec 17sec 11sec 37.4 seconds
Total Plot Area Plot # 1 Length x Width 1.43m x .7m Total Area 1 m2
Inter-territorial behavior None, because no other gobies occupied pool #4.
Conclusion
Gobies are commonly found on volcanic islands. Dominica, being a volcanic island, is home to many gobies in different streams, lakes and brackish environments. The species Sicydiinae is seemed to be the most abundant in the Checkhall River. The gobies found in the Checkhall River were territorial in the sense that they occupied one space or territory in a pool. Through observation the gobies were found to occupy that territory day after day. The inter-territorial behavior or neighboring gobies showed that most often they ignored one another but would attack and give chase, which was rare. Also they exhibited random feeding behavior. Their times spent on rocks in their territory were not consistent. They also went from rock to rock without any system or method, landing by chance, but still within their territory.
Works Cited
http://www.fishbase.org Murdy, E.O. and D.F. Hoese, 2002. Gobiidae. Gobies. p. 1781-1796. Murdy, E.O. and D.F. Hoese, 2004. Gobiidae. Gobies. p. 1781-1782.