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Hardhead catfish
The hardhead catfish (Ariopsis felis) is a species of sea catfish from the northwest Atlantic and Gulf of Mexico, and similar to the gafftopsail catfish (Bagre marinus). It is one of four species in the genus Ariopsis. The common name, hardhead catfish, is derived from the presence of a hard, bony plate extending rearward toward the dorsal fin from a line between the catfish's eyes. It is an elongated marine catfish that reaches up to 28 in (70 cm) in length and 12 lb (5.5 kg) in weight. Their typical weight is less than 1 lb (450 g), but they commonly reach up to 3 lb (1.4 kg). They are often a dirty gray color on top, with white undersides.
Hardhead catfish are found mostly in the near-shore waters of the Western Atlantic Ocean, around the southeast coast of the United States, around the Florida Keys and the coast of the Gulf of Mexico. Hardhead catfish are also found in brackish estuaries and river mouths where the bottom is sandy or muddy, but only occasionally enter freshwater. It tends to move from shallower to deeper waters in the winter months. The species is generally common to abundant within its range.
The hardhead catfish has four barbels under the chin, with two more at the corners of the mouth. These barbels help the catfish find crabs, fish, and shrimp in the muddy or sandy bays where they live. The head is slightly flattened and conceals a hard plate between the eyes and dorsal fin. The dorsal and pectoral fins each are supported by a sharp, slime-covered, barbed spine. The dorsal spine is normally erect when the fish is excited and a tennis shoe or even a leather-soled shoe offers little protection. The gafftopsail catfish looks similar to the hardhead catfish, but its dorsal and pectoral spines have a distinctive fleshy extension (like the fore-and-aft topsail of a ship).[citation needed]
A. felis consumes a wide range of food. It is an opportunistic consumer that uses mud and sand flats as hunting grounds. It is also mainly a secondary consumer, ingesting primarily detritus, meio-, and macrobenthic fauna, and fish. Its diet primarily consists of algae, seagrasses, cnidarians, sea cucumbers, gastropods, polychaetes, shrimp, and crabs. It can occasionally be a tertiary consumer.
Its diet depends on its size and location. Younger hardhead catfish tend to eat small crustaceans, like amphipods, shrimp, blue crabs, mollusks, and annelids. Juveniles that are still under the protection of the male mouthbrooder feed predominately on planktonic crustaceans close by to the mouth of the parent. The adults primarily consume larger fish.
Significant evidence suggests correlation between the fish's activity patterns and seasonal changes. Under controlled conditions of photoperiod, temperature, and water quality, hardhead catfish display nonrandom oscillations in angular orientation of locomotive activity. There appears to be annual, bimodal cycles for all three of these variables. The cycles match with the seasonal inshore-offshore migrations of hardhead catfish. Photoperiod appears to be the exogenous cue that triggers the cyclic changes in behavior. The presence of this seasonal behavior indicates that a circadian neural mechanism may exist in hardhead catfish.
Hardhead catfish respond to chemicals released by injured individuals with increased activity, illustrating communication among catfish. Their activity level was highest right after the onset of the chemical stimulus. They also respond to chemical cues from injured sailfin mollies, but this response was weaker than that of the response from their own species. After examining the epidermis of the hardhead catfish, the alarm substance cells apparently were similar to those of freshwater catfish. These chemical responses had only been seen in freshwater ostariophysans. Hardhead catfish are the first marine ostariophysans found to elicit this type of alarm reaction.
Furthermore, hardhead catfish are the first indicator that Osteichthyes possibly could use directional hearing to detect obstacles. Emissions of low-frequency sounds were related to the detection and avoidance of close obstacles. Individuals within the group that produced sound avoided obstacles, whereas silent individuals crashed into obstacles frequently. Many fish have been associated with sound production for alarm, territorial, and courtship purposes, but sound probing of surroundings seems to be only be seen in hardhead catfish. So far, no evidence exists for far-field echolocation, such as seen in bats or toothed whales. The signal parameters have low frequency and amplitude, so far-field reverberations are unlikely to be useful. If echolocation exists, it is likely only useful in the near field by the catfish.
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Hardhead catfish
The hardhead catfish (Ariopsis felis) is a species of sea catfish from the northwest Atlantic and Gulf of Mexico, and similar to the gafftopsail catfish (Bagre marinus). It is one of four species in the genus Ariopsis. The common name, hardhead catfish, is derived from the presence of a hard, bony plate extending rearward toward the dorsal fin from a line between the catfish's eyes. It is an elongated marine catfish that reaches up to 28 in (70 cm) in length and 12 lb (5.5 kg) in weight. Their typical weight is less than 1 lb (450 g), but they commonly reach up to 3 lb (1.4 kg). They are often a dirty gray color on top, with white undersides.
Hardhead catfish are found mostly in the near-shore waters of the Western Atlantic Ocean, around the southeast coast of the United States, around the Florida Keys and the coast of the Gulf of Mexico. Hardhead catfish are also found in brackish estuaries and river mouths where the bottom is sandy or muddy, but only occasionally enter freshwater. It tends to move from shallower to deeper waters in the winter months. The species is generally common to abundant within its range.
The hardhead catfish has four barbels under the chin, with two more at the corners of the mouth. These barbels help the catfish find crabs, fish, and shrimp in the muddy or sandy bays where they live. The head is slightly flattened and conceals a hard plate between the eyes and dorsal fin. The dorsal and pectoral fins each are supported by a sharp, slime-covered, barbed spine. The dorsal spine is normally erect when the fish is excited and a tennis shoe or even a leather-soled shoe offers little protection. The gafftopsail catfish looks similar to the hardhead catfish, but its dorsal and pectoral spines have a distinctive fleshy extension (like the fore-and-aft topsail of a ship).[citation needed]
A. felis consumes a wide range of food. It is an opportunistic consumer that uses mud and sand flats as hunting grounds. It is also mainly a secondary consumer, ingesting primarily detritus, meio-, and macrobenthic fauna, and fish. Its diet primarily consists of algae, seagrasses, cnidarians, sea cucumbers, gastropods, polychaetes, shrimp, and crabs. It can occasionally be a tertiary consumer.
Its diet depends on its size and location. Younger hardhead catfish tend to eat small crustaceans, like amphipods, shrimp, blue crabs, mollusks, and annelids. Juveniles that are still under the protection of the male mouthbrooder feed predominately on planktonic crustaceans close by to the mouth of the parent. The adults primarily consume larger fish.
Significant evidence suggests correlation between the fish's activity patterns and seasonal changes. Under controlled conditions of photoperiod, temperature, and water quality, hardhead catfish display nonrandom oscillations in angular orientation of locomotive activity. There appears to be annual, bimodal cycles for all three of these variables. The cycles match with the seasonal inshore-offshore migrations of hardhead catfish. Photoperiod appears to be the exogenous cue that triggers the cyclic changes in behavior. The presence of this seasonal behavior indicates that a circadian neural mechanism may exist in hardhead catfish.
Hardhead catfish respond to chemicals released by injured individuals with increased activity, illustrating communication among catfish. Their activity level was highest right after the onset of the chemical stimulus. They also respond to chemical cues from injured sailfin mollies, but this response was weaker than that of the response from their own species. After examining the epidermis of the hardhead catfish, the alarm substance cells apparently were similar to those of freshwater catfish. These chemical responses had only been seen in freshwater ostariophysans. Hardhead catfish are the first marine ostariophysans found to elicit this type of alarm reaction.
Furthermore, hardhead catfish are the first indicator that Osteichthyes possibly could use directional hearing to detect obstacles. Emissions of low-frequency sounds were related to the detection and avoidance of close obstacles. Individuals within the group that produced sound avoided obstacles, whereas silent individuals crashed into obstacles frequently. Many fish have been associated with sound production for alarm, territorial, and courtship purposes, but sound probing of surroundings seems to be only be seen in hardhead catfish. So far, no evidence exists for far-field echolocation, such as seen in bats or toothed whales. The signal parameters have low frequency and amplitude, so far-field reverberations are unlikely to be useful. If echolocation exists, it is likely only useful in the near field by the catfish.
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