Toxotes Chatareus Research Articles

Trophic position of archerfish species (Toxotes chatareusandToxotes jaculatrix) in the Malaysian estuaries

Summary The study objectives were to identify (i) the diet composition of two co-occurring archerfish species (Toxotes chatareus and Toxotes jaculatrix), (ii) their potential food preferences, and (iii) their overall trophic level in Malaysian estuaries. For this purpose the stomachs of 128 archerfishes ranging in size of 9.8–22.5 cm and 8.7–23 cm, respectively, were examined from selected Malaysian estuaries. Crustaceans, in particular red clawed crab (Sesarma bidens), occurred in the majority of stomachs and constituted 72.55 and 66.43% of the diet by weight in T. chatareus and T. jaculatrix, respectively. Insects were mostly Formicidae, Dytiscidae, Araneidae, and Cerambycidae and occurred in 10.8, 12.0; 5.1, 6.3; 4, 5.3; 3.2, 1.7% in T. chatareus and T. jaculatrix species and constituted the second most important food category consumed. Other crustaceans and shrimp (Penaeus sp.) constituted 4.4 and 2.7% of the diet by weight and were the third most important food type consumed by the two species. Moreover, these species hardly ever exhibited cannibalistic traits; Toxotes spp. comprised only 5.5% of stomach contents and was observed only in the T. jaculatrix species. Stomach content and trophic level analysis denoted that T. chatareus and T. jaculatrix are strongly carnivorous species. Furthermore, diets did not differ significantly between sizes or sexes and geographic location.

Population growth, trophic level, and reproductive biology of two congeneric archer fishes (Toxotes chatareus, Hamilton 1822 and Toxotes jaculatrix, Pallas 1767) inhabiting Malaysian coastal waters

Population growth, trophic level, and some aspects of reproductive biology of two congeneric archer fish species, Toxotes chatareus and Toxotes jaculatrix, collected from Johor coastal waters, Malaysia, were studied. Growth pattern by length-weight relationship (W=aL(b)) for the sexes differed, and exhibited positive allometric growth (male, female and combined sexes of T. chatareus; female and combined sexes of T. jaculatrix) and isometric growth (male samples of T. jaculatrix only). Trophic levels of both species were analyzed based on 128 specimens. The results show that, in both species, crustaceans and insects were the most abundant prey items, and among crustaceans the red clawed crab Sesarma bidens and Formicidae family insects were the most represented taxa. The estimated mean trophic levels for T. chatareus and T. jaculatrix were 3.422+/-0.009 and 3.420+/-0.020, respectively, indicating that they are largely carnivores. Fecundity of T. chatareus ranged from 38 354 to 147 185 eggs for females with total length ranging from 14.5 to 22.5 cm and total body weight from 48.7 to 270.2 g, and T. jaculatrix 25 251 to 150 456 eggs for females with total length ranging from 12.2 to 23.0 cm and total body weight from 25.7 to 275.0 g. Differences in values of gonadosomatic and hepatosomatic indexes calculated for both species in this study may have resulted from uneven sample size ranges.

Measuring and tracking eye movements of a behaving archer fish by real-time stereo vision

The archer fish (Toxotes chatareus) exhibits unique visual behavior in that it is able to aim at and shoot down with a squirt of water insects resting on the foliage above water level and then feed on them. This extreme behavior requires excellent visual acuity, learning, and tight synchronization between the visual system and body motion. This behavior also raises many important questions, such as the fish's ability to compensate for air–water refraction and the neural mechanisms underlying target acquisition. While many such questions remain open, significant insights towards solving them can be obtained by tracking the eye and body movements of freely behaving fish. Unfortunately, existing tracking methods suffer from either a high level of invasiveness or low resolution. Here, we present a video-based eye tracking method for accurately and remotely measuring the eye and body movements of a freely moving behaving fish. Based on a stereo vision system and a unique triangulation method that corrects for air–glass–water refraction, we are able to measure a full three-dimensional pose of the fish eye and body with high temporal and spatial resolution. Our method, being generic, can be applied to studying the behavior of marine animals in general. We demonstrate how data collected by our method may be used to show that the hunting behavior of the archer fish is composed of surfacing concomitant with rotating the body around the direction of the fish's fixed gaze towards the target, until the snout reaches in the correct shooting position at water level.

Age Determination of Archer Fishes (Toxotes jaculatrix and Toxotes chatareus) Inhabiting Malaysian Estuaries

In this study the most common bony structure (scales) and method was investigated for age determination of archer fishes. A total of 85 specimens of archer fishes (Toxotes chatareus and Toxotes jaculatrix) from the estuaries of South Johore, Malaysia were examined for age. Scale length is linearly proportion (r = 0.816) to standard length (SL). Relationship between scale length (L) and scale weight (W) can be expressed by the formula W = 0.0155L2.917. Daily growth rings and annulus of scales count up demonstrated that the ages of the samples for both species were mostly 1-2 years and a handful samples of T. jaculatrix were above 2 years.

Length-Weight and Length-Length Relationships of Archer and Puffer Fish Species

Length-weight and length-length relationships are presented for four fish species from the estuaries of south Johore, Peninsular Malaysia. The values of the exponent b in the length-weight relationships (LWRs) W= aL b ranged from 2.97 to 3.44 and length-length relationships (LLRs) TL= aSL b ranged from 0.87 to 0.95. The application of these re- gressions should be limited to the observed length ranges. The condition factor K was judged to be less important in com- parative studies, since this parameter was closely correlated with b. To our knowledge the length-weight and length-length relationships presented herein for both archer fish (Toxotes chatareus and Toxotes jaculatrix) and puffer fish (Lagocepha- lus wheeleri and Lagocephalus sceleratus) species collected from study area represents the first reference available in Ma- laysian waters.

The fishes of Lake Kununurra, a highly regulated section of the Ord River in northern Western Australia

The Ord River, situated in the east Kimberley region of Western Australia, is regulated by two darns that supply irrigation water for tropical agriculture. The regulation of water in the 55 km span of river between these dams has resulted in this section now resembling a lacustrine rather than riverine environment that is reflected in its name, Lake Kununurra. Utilising various sampling techniques we captured/observed 4157 fish from 19 species in 13 families, whilst the presence of a further three species was confirmed by reliable sources. Nematalosa erebi, Craterocephalus stramineus and Melanotaenia austrahs were the three most widespread and abundant species, being encountered throughout the lake and representing -66% of all fish recorded. Ambassis sp., Arius midgleyi, A. graeHei, Glossamia aprion, Amniataba percoides, Hephaestus jenkinsi, Glossogobius giurus and Toxotes chatareus were found throughout the lake but generally at fewer sites and in smaller numbers (-30% of all fish) than the three dominant species. The remaining species Neosilurus ater, Strongylura kreHtii, Leiopotherapon unicolor, Syncomistes but/eri, Lates calcari{er, Mogumda mogumda, Oxyeleotris lineolatus and Ambassis madeayi were generally found at few sites and in low numbers, and accounted for less than 4% of the overall catch. The regulation of the Ord River has apparently altered the species composition and abundances in Lake Kununurra. For example, marine/estuarine species, commonly encountered in the freshwaters of large northern Australian Rivers, are largely absent, while species such as L. unicolor, which is one of the most abundant species in nearby rivers and tropical Australian rivers in general, contributed to <1°/,) of the total catch.

Archer Fish Learn to Compensate for Complex Optical Distortions to Determine the Absolute Size of Their Aerial Prey

Many animals, including humans, can visually judge the absolute size of objects regardless of changes in viewing distance and thus despite the resulting dramatic differences in the size of the actual retinal images. For animals that have to judge the size of aerial objects from underwater views, this can be a formidable problem; our calculations show that considerable and strongly viewpoint-dependent corrections are needed to compensate for the effects of light refraction. Archer fish face these optical difficulties because they have to shoot down aerial insects over a wide range of horizontal and vertical distances. We show here that these fish can learn to acquire size constancy with remarkable precision and are thus fully capable of taking complex viewpoint dependency into account. Moreover, we demonstrate that archer fish solve the problem not by interpolating within a set of stored views and distances but by learning the laws that connect apparent size with the fish's relative position to the target. This enables the fish to readily judge the absolute sizes of objects from completely novel views.

Prey catching in the archer fish: angles and probability of hitting an aerial target

When trying to squirt down aerial arthropods, archer fishes (Toxotidae) have to cope with the displacement of the image of the target by refraction of light at the water surface. It has been suggested, and accepted, that Toxotes jaculatrix would avoid the effect of refraction by squirting vertically. In our previous study, however, Toxotes chatareus was observed to squirt under a wide range of angles, including angles much smaller than 90°. The aim of the present study was to asses in T. chatareus ( N=15), the frequency distribution of angles used, the relation between angle and probability to hit, the relation between target height and angle, and the smallest angles the fishes can use. The outcome was a distribution with a range of 102–58° and a median of 74°, no relation between angle and probability to hit, no relation between target height and angle and a smallest angle of 45°. The results clearly indicate that T. chatareus does not evade the refraction effect by squirting only vertically (90°), but masters a considerable refraction effect thanks to a mechanism that is not investigated here. The capacity to hit prey under a wide range of angles is seen as an important adaptation to the natural habitat where the visibility of prey is restricted by vegetation. The constraints of the range of angles are discussed.

Refraction and the spitting behavior of the archerfish (Toxotes chatareus)

1. Archerfish (Toxotes chatareus) spit droplets of water at aerial insect prey, knocking them onto the water surface to be eaten. Since the fish's eyes remain completely below the water surface during sighting and spitting the fish must deal with potentially severe refraction effects at the air-water interface. High speed (200 f.p.s.) motion picture films of 480 spitting sequences were analyzed to determine the magnitude of the refraction effect and to suggest how the fish compensate for it. 2. T. chatareus do not shoot from a position directly below the prey, but can correctly set their spitting angle to compensate for the refraction unique to a variety of positions (Fig. 6). The fish can correct (Fig. 14) for large refraction effects on the prey's apparent elevation (Fig. 12) or apparent height (Fig. 13). They may be enabled to do so by a rather precise linear relationship between the real elevation of the prey from the nose and the apparent elevation from the eye which exists during sighting (Fig. 15) and spitting. However, spitting accuracy decreases with increasing prey height (Fig. 7) or range (Fig. 8). 3. The archerfish must also correct for significant curvature of the water droplet's trajectory (Fig. 10). Since shot velocity is relatively constant (Fig. 9) the fish must make this correction via their spitting angle, but the stage in the spitting process at which this occurs is unknown.