Brett Mommer and Xuan Zhuang

phylogenetic tree of the fishes

Unifying features of Scombroidei Non-protractile mouth (a secondary loss) Torpedo shape streamlined for fast swimming Extremely active group of (mostly) oceanic pelagic fishes found in tropical, subtropical, and temperate marine habitats. All are highly predacious! This group makes up about 10% of marine catches.

Class Actinopterygii –Order Perciformes Suborder Scombroidei – 6 families (in no particular order) –Scombridae – mackarels, tunas, bonitos –*Xiphiidae – swordfish –*Istiophoridae – sailfish, marlin, spearfish –Sphyraenidae – barracudas –Gempylidae – snake mackerels –Trichiuridae – cutlassfishes *Some believe Xiphiidae and Istiophoridae belong to a separate suborder, Xiphioidei, the billfishes (

Dalziel et al. (2006) Molecular Evolution of Cytochrome c Oxidase in High-Performance Fish (Teleostei: Scombroidei). J. Mol. Evol. 62: Blenniidae Order Zeiformes Pholidae Messy phylogeny

Scombridae mackarels, tunas, bonitos Katsuwonus pelamis (skipjack tuna) Scomberomorus cavalla (carite lucio)Acanthocybium solandri (peto) Scomber scombrus (Atlantic mackerel) 15 genus, 51 species15 genus, 51 species

Scombridae –tunas

Scombridae – mackarels, tunas, bonitos As tuna are often caught great distances from where they are processed, poor quality control may lead to spoilageAs tuna are often caught great distances from where they are processed, poor quality control may lead to spoilage

Tuna Morphology: streamline shape body, dorsal fin can be hidden within the groovesMorphology: streamline shape body, dorsal fin can be hidden within the grooves pink to dark red flesh greater quantities of myoglobinpink to dark red flesh greater quantities of myoglobin high oxygen demand high oxygen demand Tuna fastest swimmers in the ocean (60 mph)

fishes swim in straight lines at a high rate of speed with the mouth open.fishes swim in straight lines at a high rate of speed with the mouth open. forces water through the mouth and over the gillsforces water through the mouth and over the gills breathe passively while swimmingbreathe passively while swimming an effective way of respirationan effective way of respiration Ram ventilation In fish which have a reduced or no ability to pump water into their mouth, keeping swimming is required to maintain ventilation.

Warm-blooded  Some of the larger tuna species are warm-blooded, such as the bluefin tuna, they can maintain their blood temperature much higher than the water temperature.

Regional heterothermy A specialized type of endothermy present in tunas, billfish, and some sharks (convergence!). Oxidative “red” muscle in core of fish (cruising), surrounded by glycolytic “white” muscle (sprinting). As predators, they can “maintain aerobic swimming at a speed which the prey has begun to sprint anaerobically” (Katz, 2002). Advantages of endothermy w/o cost of maintaining elevated overall metabolic rate (Helfman et. al). Non-heterotherm Heterotherm

Regional heterothermy Maintain a roughly constant thermal gradient 4-20°C above ambient Heat produced from red muscle contraction improves muscle power output. Also a complex circulatory anatomy to deliver O2 and prevent conduction of heat away from red muscle. Our old friend, The rete!

Effectiveness vs. Efficiency Katz, Stephen L. (2002) Design of heterothermic muscle in fish. J. of Exp. Biology. 205: Non-Hetero Hetero Energetically less efficient (to have increased red muscle), but more effective in open sea where there’s nowhere for prey to hide!

Tuna associate with dolphins to avoid sharkassociate with dolphins to avoid shark heavy metals can be high in larger speciesheavy metals can be high in larger species High position in the food chain High position in the food chain Subsequent accumulation Subsequent accumulation

Tuna Fishing important commercial fishimportant commercial fish some stocks are at risk of collapse due to overfishingsome stocks are at risk of collapse due to overfishing

Xiphiidae – swordfish sharp bill (sword):sharp bill (sword): not used to spear,not used to spear, but instead may be used to slash at its preybut instead may be used to slash at its prey or defend against its predatoror defend against its predator olympic octopus and swordfish fencing

Xiphiidae – swordfish Breaching: powerful jumping from the oceanBreaching: powerful jumping from the ocean dislodge parasites ----remoras or lampreysdislodge parasites ----remoras or lampreys

Xiphiidae – swordfish Age: can live to be more than 25 years oldAge: can live to be more than 25 years old Weigh: as much as 1,200 poundsWeigh: as much as 1,200 pounds Don’t have either scales or teeth.Don’t have either scales or teeth.

Xiphiidae – swordfish swim alone or in a very loose groupingswim alone or in a very loose grouping feed on: squid, tuna and mackerelfeed on: squid, tuna and mackerel few natural predators: large sharks & whalesfew natural predators: large sharks & whales

Istiophoridae – sailfish, marlin, spearfish 3 genus, 11 species3 genus, 11 species

sailfish  distinctive dorsal fin: like a sail folded down to the side when swimmingfolded down to the side when swimming raised when feeling threatened or excitedraised when feeling threatened or excited during feeding, a group of sailfish use their sails to "herd" a school of fishduring feeding, a group of sailfish use their sails to "herd" a school of fish

Marlin 16 ft in length, 1500 lb in weight16 ft in length, 1500 lb in weight

“Heater organs” Some Scombroids (22 spp) have “heater organs” around eyes, brain, and/or spinal cord. Maintain tissues 10 to 15 C° above ambient. Modified ocular muscle cells that don’t contract, but Pump Ca ++ in a loop, burning ATP & creating heat (many mitochondria) Associated with rete mirabiles; retain heat within blood using countercurrent-exchange. Greatly improves vision, ability to catch prey in cold temps. Protects CNS from temperature fluctuations during vertical travel. Different eye muscles modified as heater organs in different groups, thought to be independently evolved. Some Scombroids (22 spp) have “heater organs” around eyes, brain, and/or spinal cord. Maintain tissues 10 to 15 C° above ambient. Modified ocular muscle cells that don’t contract, but Pump Ca ++ in a loop, burning ATP & creating heat (many mitochondria) Associated with rete mirabiles; retain heat within blood using countercurrent-exchange. Greatly improves vision, ability to catch prey in cold temps. Protects CNS from temperature fluctuations during vertical travel. Different eye muscles modified as heater organs in different groups, thought to be independently evolved.

“Heater organs” EYE Heater organ Rete Brain Anterior Metrio et. al. (1997) Heat-Producing Organ of the Swordfish (Xiphius gladius): A Modified Eye Muscle. J. of Morphology 234:89-96

Sphyraenidae – barracudas public domain - U.S. National Oceanic and Atmospheric AdministrationNational Oceanic and Atmospheric Administration 1 genus, 20 species Considered primitive members of Scombroidei Tropical and subtropical oceans, also reefs. Ambush predators, bursts up to 27 mph. Up to 6 ft in length.

Gempylidae – snake mackerels 23 species Pelagic and deepwater predators Elongate body, long spiny dorsal fin, posterior finlets. large mouth, long teeth. Commercially fished

Trichiuridae – cutlassfishes 40 species, shallow coastal waters worldwide. Lost finlets, pelvic, anal, and most of caudal fin. Fanglike teeth, eat zoops, fish, crustaceans. Adults feed near surface during day, migrate to bottom at night. Juveniles do the opposite. Can be over 2 meters long.

Population declines of predatory fish communities Estimate current level ~10% preindustrial. Industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation. Management based on recent data alone may be misleading; there is no “baseline”. Myers, R.A. and B. Worm Reply to Decline of Pacific tuna populations exaggerated? Nature. 434: E2.

Worldwide Population Declines Myers, R.A. and B. Worm Reply to Decline of Pacific tuna populations exaggerated? Nature. 434: E2. Tuna, Billfishes, Swordfish Data from Japanese Pelagic Longlining

ICCAT The International Commission for the Conservation of Atlantic Tunas is an inter-governmental fishery organization responsible for the conservation of tunas and tuna-like species in the Atlantic Ocean and its adjacent seas. Set a MSY (Maximum Sustainable Yield), but many people outraged that ICCAT continues to allow overfishing/longlining, especially by Japan. Western Atlantic Bluefin Tuna currently at 3% pre- longlining population; same story for other spp. A single bluefin sold for $172,400 at the first auction of 2001 at Tokyo's Tsukiji Fish Market. Lawsuits filed to protect spawning areas and put on endangered species list...

Review Questions What about the biology of tuna and other scombroids makes them vulnerable to overexploitation? Why should we worry about declining tuna populations? What advantage do endothermic Scombroids have over fish without endothermy? If endothermy is so great, why not commit to it? That is, what advantage does regional heterothermy have over complete endothermy? What is Ram ventilation? Which fish groups can it be found? How does it help those fishes to get oxygen? Why do researchers think heater organs evolved multiple times in Scombroids? How do heater organs differ from red muscle in the way heat is created? Why swordfishes like to jump from the ocean?