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Jacks & andere zilverachtige vissen
Groep 2 - Zilverachtig: Zilverachtige vissen hebben veel verschillende familieleden, hoewel we slechts een paar vertegenwoordigers zullen bekijken. In tegenstelling tot de kleurrijke vlinder-, engel- en doktersvis passen de zilvervissen beter op in open water en worden ze meestal niet in de buurt van de kleurrijke bodem aangetroffen.
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”)
Bigeye Jack (jurel ojón, Caranx sexfasciatus)
These large-bodied jacks are a relatively common sight in the southern Gulf of California all the way down to the Galapagos. The ID key is the large eye and the white tip on the dorsal fin. They have a steep forehead and are often seen in schools. (Size 1-2 feet, max. 2.5 ft)
Cortez Chub (chopa de Cortes, Kyphosus elegans)
Chubs are characteristically
football shaped and a dark gray in color. They feed on algae and plankton drifting near the surface. Because of the small food size they have very small mouths for their body size and small, chubby cheeks along side. The Cortez chub has a long anal fin like the long Sea of Cortez. (Size 6-12”, max 15”)
football shaped and a dark gray in color. They feed on algae and plankton drifting near the surface. Because of the small food size they have very small mouths for their body size and small, chubby cheeks along side. The Cortez chub has a long anal fin like the long Sea of Cortez. (Size 6-12”, max 15”)
Blue-bronze Chub (chopa, Kyphosus analogus)
The similar looking Blue- bronze chub is distinguished by an anal fin that is much trimmer to the body than in the Cortez chub. If you draw an imaginary line along the anal fin it would pass into the tail, whereas the same line in the Cortez chub would pass in front of the tail. (Size 6-12”, max 18”)
Mexican Barracuda (picuda agujona, Sphyraena lucasana)
The barracuda is rarely mistaken for any other fish. Tending to school together in large numbers the sleek body and large mouth are perfect for catching the small fish that it feeds on. This is a close up picture, but the next image illustrates how you will usually encounter the Mexican barracuda, from below. To see these schooling fishes, you need to look up into the water column as they are rarely found down on the reef. (Max. size 2.5 feet)
Black Jack (Caranx lugubris)
The black jack is a large fish, and is known to grow to a length of 1 m and a weight of 17 kg, although is more common at lengths under 70 cm. The body of the black jack is a uniform olive to brown, grey and even black colour along the back that lightens to a grey-blue near the underside of the fish. The black jack's fins are grey to black, and the scutes are black. The upper limit of the operculum often has a small dark spot present, usually smaller than the pupil.
Rainbow Runner (Elagatis bipinnulata)
The colour of the fish is possibly the easiest way to identify the rainbow runner, with the name taken from the species' striking colours. The upper body is a dark olive blue to green and fades to white underneath. Two narrow, light blue to bluish white stripes run longitudinally along the sides, with a broader olive to yellow stripe between them.
Almaco Jack (Seriola rivoliana)
The longfin yellowtail has a less elongated, more flattened body than most jack species. Their dorsal fin and anal fins are elongated, and their outer edges have a definite sickle shape. The first rays of the almaco dorsal fin's longest parts are nearly twice as long as the dorsal spines, also different from other jacks.
They reach a typical length of 90 centimetres.
They reach a typical length of 90 centimetres.
Gafftopsail Pompano
(Trachinotus rhodopus )
A species of jack in the family Carangidae. It is found in the eastern Pacific. The maximum size for this fish is 61 centimetres (24 in) but usually grows up to 25 centimetres (9.8 in). It is diamond shaped with yellow fins. The colouration of this fish is silver.
Milkfish (Chanos chanos)
The milkfish can grow to 1.80 m (5 ft 11 in), but are most often no more than 1 m (39 in) in length. They can reach a weight of about 14 kg (31 lb). and an age of 15 years. They have an elongated and almost compressed body, with a generally symmetrical and streamlined appearance, one dorsal fin, falcate pectoral fins and a sizable forked caudal fin. The head is small relative to the body. The mouth is small and toothless. The body is olive green, with silvery flanks and dark bordered fins.
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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.
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