A Definitive Key to Identify African Tiger Fish (Hydrocynus)

This article is dated. Please refer to the new version here:

http://www.monsterfishkeepers.com/f...and-ID-of-African-Tiger-Fish-(Hydrocynus)-2-1

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A Definitive Guide to Identifying African Tiger Fishes (Hydrocynus) in Aquaria.

I am writing this post in an effort to clarify the five species of African tiger fish (ATF) in home aquaria. I have hopes that this will be stickied to help other people identify their fish.

On this site and others, it has been my observation that anything without stripes or with poorly formed stripes has been identified as Hydrocynus goliath and anything having well formed stripes has been identified as being Hydrocynus vittatus. Based on my studies over the past few months, I do not feel that this is correct and I am seeking to clarify this issue based on research that I have done in scientific journals and the conclusions I have drawn from said research. If the conclusions I draw do not agree with the current Hydrocynus identification thread then it can be assumed that I am directly challenging its conclusions and would like to see verifiable evidence that I am wrong.

Contents:

Key to identification
Hydrocynus goliath
Hydrocynus tanzaniae
Hydrocynus brevis
Hydrocynus vittatus
Hydrocynus forskahlii
References

All photos used throughout this guide are the property of their owners and were retrieved from the public domain.

Key to identification:

Click on species name to go to that profile.

Hydrocynus goliath: Silvery. Little or no striping. Red colored tail normally only on bottom lobe. Large, straight head. LL scale count 53-58. Anal fin rays 3 & 12.

Hydrocynus tanzaniae: Greyish. Pronounced striping. Blue or green colored tail. Dark, steel blue adipose fin. LL scale count 43-47. Anal fin rays 3 & 12-13.

Hydrocynus brevis: Silvery or golden, shiny. Little or no striping. Very large adipose fin in relation to body. Dark gray tail with dark red lower lobe. Very thick body. LL scale count 47-55. Anal fin rays 3 & 11-13.

Hydrocynus vittatus: Silvery white. Dramatic striping. Red, orange or yellow tail with color on both lobes. Noticably thicker body than the very similar H. forskahlii. LL scale count 45-50. Anal fin rays 3 & 11-12.

Hydrocynus forskahlii: Silvery white. Dramatic striping. Red, orange or yellow tail with color ONLY on the lower lobe. Noticeably more slender in build than the very similar H. vittatus. LL scale count 46-53. Anal fin rays 3 & 11-14.

View attachment 844135
Picture credit to Goodier, Cotterill, O’Ryan & Skelton, 2011.

Species profiles:

Hydrocynus goliath (GATF)

The GATF is the largest species of Hydrocynus. It has the least distinctive stripes of the genus. It has between 53 and 58 scales on the lateral line. The anal fin has 3 soft, unbranched rays and usually 12 branched rays. The dorsal profile of the head is straight. The depth of the body in adults is 19.4 to 32.7 percent of the length, with an average of 23 percent. The length of the head is 19.2 to 23.1 percent of the total length. The teeth can have between 12-20 in the upper jaw and 8-14 in the lower jaw. This wide variation is due to their having several small teeth that may or may not protrude through the gums near the back of the mouth (Brewster, 1986). These fish are silvery in color with a red tail that often only has color on the lower lobe. Coloration will often be washed out in extremely young individuals. The range of the GATF is from the Congo River drainage basin (Goodier, Cotterill, O’Ryan & Skelton, 2011). The IGFA expects that the largest Goliath tigerfish may exceed 110 pounds, up to a potential maximum of 132 pounds. The current all tackle world record is 97 pounds.


Baby at approximately 3 inches.


Young fish of about 8 inches.


Large adult.

Hydrocynus tanzaniae (TATF)

TATF have pronounced stripes. They have 43-47 lateral line scales. They are distinct from the rest of the species in the genus by having elongated third and fourth dorsal and anal fin rays. The anal fin has 3 soft, unbranched anal fin rays and 12 or 13 soft, branched anal fin rays. The body has a mean depth ratio of 23.8 percent of the standard length, with a range of 20.0 to 26.6 percent. The length of the head is 18.3 to 22.2 percent of the body length. TATF have 13-16 teeth in the upper jaw and 10 to 12 in the lower jaw (Brewster, 1986). TATF have a silvery-gray body with dark stripes. Their caudal fin can be blue or green. They often have various markings of blue, green, grey, pink or red. TATF have a steel blue adipose fin, although this may not be obvious when young or without bright lighting. Coloration will often be washed out in extremely young individuals. Hydrocynus tanzaniae are from the eastward flowing rivers in Tanzania; the Rufiji and Ruasha watersheds (Brewster 1986; Goodier et al., 2011). The IGFA does not currently recognize a world record for the TATF, but fish have been caught in excess of 27 inches and 25 pounds.


Baby of about 2.75 inches.


Young fish at about 6 inches.

ATTACH=CONFIG]844148[/ATTACH]
A large specimen of indeterminate size. Note that this picture is too dark to show the color well.


An adult specimen.

Hydrocynus brevis (BATF)

Except for Hydrocynus goliath, BATF has the least developed striping of all members of the genus. BATF have a lateral line scale count of 47-55. Anal fin ray count 3 soft, unbranched rays with 11-13 branched rays. BATF on average has the deepest body to length ratio with an average of 24.4 percent and a range of 19.1 to 29.6 percent of the total length. BATF have 10 to 12 teeth in the upper jaw and 8 to 13 in the lower jaw (Brewster, 1986). BATF have a golden or silvery base color with tan or grey paired fins. The adipose fin is often very large in relation to the other ATF species. Their caudal fin has a base of dark gray with a very dark red lower lobe. Coloration will often be washed out in extremely young individuals. Hydrocynus brevis are from northeast Africa with an range that often overlaps Hydrocynus forskahlii. They are primarily from the watersheds of the Nile and Niger rivers. The IGFA recognizes the largest all-tackle BATF as 12 pounds, eight ounces; but a 28 pound, 9 ounce specimen is being considered as the new world record fish.


Baby at about 3 inches.

View attachment 844137
Medium sized young fish at about 8-10 inches.


This fish is 28 pounds, 9 ounces and is being considered by the IGFA as a new world record. Photo credit to the IGFA.


Comparison of sympatric species H. brevis and H. forskahlii. BATF on top, FATF below.

Hydrocynus vittatus (VATF)

VATF have pronounced stripes. They have a lateral line scale count of 45-50. They have an anal fin ray count of 3 soft, unbranched rays and 11 to 12 branched rays. Body depth ratios were not elaborated upon in the description, but it was noted that “H. vittatus seems generally more massive than H. forskahlii” (Paugy, Guegan, 1989). Exact numbers of teeth are not elaborated upon in the description by Paugy and Guegan (1989). VATF are a bright, whitish silvery color. They can have red, orange or yellow caudal fins with both lobes having color. The center of the caudal fin, regardless of color, is often red. Paired fins are often pale yellow or orange. The anus is often orange or red (Paugy et al., 1989; Goodier et al., 2011). Coloration will often be washed out in extremely young individuals. It is interesting to note that VATF from the Upper Zambezi display sexually dimorphic coloration. Mature males had bright yellow caudal fins with bright red markings on the bottom lobe. Mature females had bright orange caudal fins (Kotze, van der Bank & Steyn, 1998). Whether or not this is applicable to all H. vittatus populations is not clear. Hydrocynus vittatus has a very wide distribution throughout Africa: they can be found in the Congo, Okavango and Chobe rivers as well as in Lake Cariba and throughout most of southern Africa (Kotze et al., 1998; Goodier et al., 2011). The IGFA holds the world record for VATF to be 35 pounds, seven ounces.

A note on the extreme variability of the VATF: Goodier et al (2011) found that there are four distinct genetic populations of Hydrocynus vittatus. These are Hydrocynus vittatus sensu stricto, or the VATF proper, and genetic populations "B, C and D". This grouping of fish is now known as the Vittatus Complex, and these fish await further description as subspecies.


A baby of about 4 inches. Note how little color is visible in the fins at this size.


Young fish of about 7 inches.


Large specimen of about 15 inches.


Adult specimen.

Hydrocynus forskahlii (FATF)

FATF have pronounced stripes. They have a lateral line scale count of 46-53 scales. Their anal fin ray count is 3 soft, unbranched rays with 11-14 branched rays. Body depth averages 22.6 percent of the length with a range of 17.2 to 27.8 percent. FATF is normally the most slender member of Hydrocynus, but girthy specimens are possible. The head averages 19.8 percent of the body length with a range of 15.3 to 25.3 percent. FATF has 9 to 14 teeth in the upper jaw and 8 to 12 in the lower jaw (Brewster, 1986). This fish often has a very short, upturned jaw. FATF are bright, silvery white in color, similar in appearance to VATF, but with a grayish caudal fin that has red, orange or yellow only on the bottom lobe of the caudal fin (Paugy et al., 1989; Goodier et al., 2011). Coloration will often be washed out in extremely young individuals. FATF often overlap H. brevis in range. They are known from northeastern Africa; the Nile basin, Senegal, Niger, Guinea and Zaire (Brewster, 1986; Paugy et al., 1989; Goodier et al., 2011). No fishing records for Hydrocynus forskahlii are readily apparent.

A note on the variability of the FATF: Goodier et al (2011) found that there are two distinct genetic populations of Hydrocynus forskahlii. These are Hydrocynus forskahlii sensu stricto, or the FATF proper, and the genetic population "E". This grouping of fish is now known as the Forskahlii Complex, and these fish await further description as subspecies.


A baby of about 2.5 inches. Note how little color is visible in the fins at this size.


A young fish of about 8 inches.


An adult specimen.

View attachment 844147
Comparison of sympatric species H brevis and H. forskahlii. BATF on top, FATF below.

References:


Brewster, B. (1986). A review of the genus Hydrocynus Cuvier 1819 (Teleostei: Characiformes). Bulletin of the British Museum (Natural History) Zoology 50(3): 163-206 (1986).


Goodier, S., Cotterill, F., O'Ryan, C., Skelton, P., de Wit, M. (2011). Cryptic Diversity of African Tigerfish (Genus Hydrocynus) Reveals Palaeogeographic Signatures of Linked Neogene Geotectonic Events. Public Library of Science, 6 (12). doi 10.1371.


Kotze, A., van der Bank, F., Steyn, G. (1998). Allozyme variation in two populations of Hydrocynus vittatus (Pisces, Characidae). South African Journal of Animal Science 28 (3/4), 153-160.


Paugy, D., Guegan, J. (1989). Note a propos de trois especes d'Hydrocynus. Revue d'Hydrobiologie Tropicale, 22 (1), 63-69.


All Tackle Species List “T”. (2012). IGFA Online WORLD RECORD SEARCH. Retrieved from: http://wrec.igfa.org/WRecSearchList.aspx?lc=AllTackle

How to figure head and body length percentages:

To do this, take a profile picture of the fish you wish to measure. I'll use a picture of my GATF for this example.

First, measure the total length of your fish (red line). Total length is defined as the length of the fish from the tip of the snout to the end of the tail when pinched together. It isn't practical for our purpose to take the fish from the tank to pinch the tail together in most circumstances, but it the difference made in most instances is inconsequential to getting a measurement if you simply go to the end of the lobe of an open tail. My fish's total length is 877 pixels.

Second, measure from the tip of the snout to the most posterior part of the operculum (gill cover). Record the number of pixels that is this length (yellow line). My fish's head length is 200 pixels.

Third, measure your fish at the tallest part of it's body (black line). Record the number of pixels this is. My fish is 168 pixels.

To get the head length percentage, divide the head's pixel number by the total pixel number to get the percentage. 200/877= 22.8%

To get the body depth percentage, divide the body's pixel number by the total pixel number to get the percentage. 168/877= 19.1

As I posted above, the head ratio for adult GATF is 19.2 to 23.1 percent and the body depth ratio is 19.4 to 32.7 percent. As you can see, my eight inch juvenile falls right at that range.