Jacks & Other Silvery Fish

Group 2: Silvery Fish

Jacks & Other Silvery

Group 2 - Silvery : Silvery fish have many different family members, though we will look at just a few representatives. As opposed to the colorful butterfly, angel and surgeonfish, the silvery fish tend to blend in better in open water and are usually not found near the colorful bottom.

Bluefin Trevally (Caranx melampygus)

The bluefin trevally is a large fish, growing to a maximum known length of 117 cm and a weight of 40 kg, The upper body of the bluefin trevally is a silver-brassy colour, fading to silvery white on the underside of the fish, often with blue hues. After they reach lengths greater than 16 cm, blue-black spots appear on the upper flanks of the fish, with these becoming more prolific with age. The species takes its name from the colour of its dorsal, anal and caudal fins, which are a diagnostic electric blue.

Green Jack (cocinero dorado, Caranx caballus)

Green jacks are small, slender members of the jack family, reaching a size of about 1 foot. Swimming rapidly in small groups near open or deep water these jacks tend to flash by divers in a hurry. The ID key is the white streak behind gill, think of it as the “green flash” at sunset. (Size 6”-12”, max. 15”)

Choose another fish Category

1. Disks and Ovals / Colorful

The first category of disk and oval shaped fish are very important to learn. They are colorful, large and very obvious and the three main families that make up the group can be found on almost every dive.

2. Silvery Fish

Silvery fish have many different family members, though we will look at just a few representatives. As opposed to the colorful butterfly, angel and surgeonfish, the silvery fish tend to blend in better in open water and are usually not found near the colorful bottom.

3. Sloping Head / Tapered Body

This third group of “fish-like” fish, are very important to learn. The are common on most dives and are also highly sought after as food fish. It is especially important to monitor these fish to provide data for fisheries management. Snappers can be very difficult to tell apart from the similarly shaped grunts. One helpful hint is to look at their tails. Snappers tend to have straight, flat tails. They are also known for their habit of snapping their mouth open and shut when caught on hook and line. They have very sharp canine teeth that can provide a nasty bite to the unsuspecting angler. Look closely on your next dive and you may see the small teeth protruding from the side of the mouth. Grunts on the other hand, have slightly notched tails. They get their name from the grunting sounds they emit when threatened. These sounds are created by rubbing together bony teeth plates located in the back of the throat. Since the teeth are in the throat, a diver will never see protruding teeth on a grunt, only big blubbery fish lips.

4. Small Ovals / Damselfish

While divers tend to first notice the larger, more obvious fish on a dive, after a short while the challenge to find new species leads them to change their search image to look for smaller, previously unnoticed fish. Generally, the first new species a diver will encounter will belong to the small oval shaped group. This group is broken into the damselfish and their close cousins the chromis. Damsels are like the surgeonfish in that they eat algae. They do not roam around grazing, but rather tend to small algae gardens like a farmer. These areas are guarded fiercely as the algae farm is the damsels food source. For that reason you can think of the damselfish as not just territorial, but Dam- selfish with its territory. Many damselfish have distinctly different colors as juveniles, often being much brighter and more colorful when they are young and becoming drab with age. (much like us humans!) For this reason, the juveniles have been heavily collected for the aquarium trade and are under heavy fishing pressure. As part of the REEF Fish Survey Project, divers are asked to monitor the juveniles and adults separately in two of the damselfish species – the Cortez damselfish and the giant damselfish.

5. Heavy Body / Large Lips

Heavy bodied, large lipped fish belong to the seabass family. We tend to refer to the larger seabasses as groupers and the smaller seabasses as bass or basslets. These fish are extremely important food fish and are under increasing threats from heavy fishing pressures. Monitoring these fish can help provide valuable data to aid in their protection. Most seabasses are hermaphrodites, meaning the same fish will be both a male and a female during its lifetime. The groupers are all born female and later change sex to become male. Most large groupers also congregate each year to spawn at a specific location, making them easy targets for emerging positioning and fishing technology.

6. Swim with Pectorals / Obvious Scales

The fish in this group all use their pectoral fins to swim with rather than the traditional tail swimming of most other fish. The scales are also quite large and obvious. These fish can also be hermaphrodites, like the groupers, with some fish changing sex and others staying the same. Intermediate and adult fish often have very different appearances compared to the always-male terminal phase. This means learning two colors to be able to ID the same species of fish. Most of the pictures shown in this curriculum are terminal phase males, unless noted.

7. Redish / Big Eyes

This group of reddish fish is normally not seen during day dives due to their nocturnal nature. The reddish color helps them blend in at night and the large eyes help them to see better.

8. Small, Elongated Bottom Dwellers

The small bottom dwelling fish often make up the most interesting fish to watch during your dive. Their approachable nature and interesting behaviors make them great fishwatching finds. Blennies tend to be slightly larger than gobies, but are most easily recognized by their curved body posture and expressive faces. Gobies, though similar in their habitat requirements, tend to sit flat and straight on the bottom. The jawfishes actually live in a burrow in the sand that they excavate and maintain.

9. Odd-Shaped Bottom-Dwellers

This category of fish is made up of families and species that didn’t quite fit anywhere else due to their unique body shapes.

10. Odd-Shaped Swimmers

This group of fish contain families that are unusual in their shape, but are swimmers rather than bottom dwellers.

11. Eels

Though looking like snakes, eels are fish. There are several different types of eels, and we will look at two – garden eels that live in burrows in the sand and moray eels. Moray eels have a bad reputation mainly due to the constant opening and closing of their sharp toothed mouths. However, this is not a threat to divers, as this action pumps water through their gills. Most eels are actually very shy.

12. Sharks & Rays

Even though the sharks and rays are cartilaginous (their skeletons are made of cartilage instead of bones), they are still referred to as fish and count during our surveys.