Sharks Honor

Nature Study

Requirements

1. What are the main differences between bony and cartilaginous fish?

   Answer: Bony fish (Osteichthyes): a rigid calcium skeleton, bony scales, an operculum covering the gills, a swim bladder controlling buoyancy, generally external fertilization, eggs with a shell; e.g.: tilapia, spotted catfish, salmon. Cartilaginous fish (Chondrichthyes): a flexible cartilage skeleton (lighter), placoid (dermal, tooth-like) scales, 5-7 gill slits without an operculum, no swim bladder (they must swim to float), internal fertilization, eggs or viviparity. — The division is taxonomically fundamental. Cartilaginous fish are more ancient evolutionarily (~450 million years). Their light structure allows fast movements. Without a swim bladder, they must swim continuously or use an oily liver to float. Bony fish dominate in diversity (>27,000 species). Cartilaginous fish are ~1,000 species. Knowing the difference guides classification. In Brazilian marine studies (Bertioga, Fernando de Noronha), both groups are studied. Sharks are the ambassadors of the cartilaginous fish.

2. Talk about the dentition of sharks and the diversity of foods they consume.

   Answer: Dentition: sharks have teeth in rows (5-15 rows depending on the species) that are continuously renewed - when one falls out, another advances from the row behind (up to 30,000 teeth over a lifetime). Teeth vary by diet: serrated triangular (hunters like the white shark), pointed (fish), flattened (crustaceans), filtering (plankton). — Dental renewal is brilliant evolution - it always maintains maximum biting capacity. Unlike humans (2 sets of teeth), sharks do not depend on dental care. Each fossil tooth is a paleontological record. Diet varies by species: the tiger shark eats 'sea garbage' (anything); the white shark attacks seals; the whale shark filters krill; the bullhead shark eats crustaceans. At camporees with a marine theme, demonstrations with fossil teeth fascinate young people. Sharks are key predators of marine ecosystems.

3. Explain how the respiration of sharks occurs.

   Answer: Sharks breathe by extracting oxygen dissolved in the water. They have 5-7 gill slits on the sides of the head (without an operculum). Most species need to swim continuously, forcing water through the mouth and expelling it through the gills (ram ventilation). Some species (angel shark, nurse shark) can breathe while stationary by actively pumping water through the mouth. — Gill respiration is evolutionarily ancient. Unlike bony fish with an operculum, sharks have visible slits. The need for continuous movement (in ~85% of species) is the reason they swim even while sleeping (some sleep with half their brain). Tuna also do this. Benthic (bottom) species pump water. In public aquariums, tanks need currents for sharks to breathe. In Brazil, the coasts have several species. Knowing respiratory biology helps in research and marine conservation.

4. Cite 2 examples of cartilaginous fish that are not sharks.

   Answer: 1) Rays (Batoidea): cartilaginous fish with a dorsoventrally flattened body, pectoral fins expanded like wings; e.g.: longnose stingray (Hypanus marianae), spotted eagle ray (Aetobatus narinari), Brazilian electric ray (Narcine brasiliensis). 2) Chimaeras (Chimaeriformes): ancient cartilaginous fish with a large head, a tapered body, two sexes (males with a clasper). — Cartilaginous fish are a diverse group. Rays represent ~600 species, more than sharks by some criteria. Some rays are giants (the manta ray, 7m wingspan). Others are tiny. Chimaeras are rare and ancient (300 million years). The sawfish is critically endangered. In Brazil, rays are common in coastal waters (beware of the venomous stinger!). Public aquariums such as AquaRio show live examples. Knowing the diversity combats the misconception that cartilaginous = only sharks.

5. Know how to identify, by means of pictures, 5 species of sharks.

   Answer: 1) Great white shark (Carcharodon carcharias): a large predator, serrated triangular teeth, white below. 2) Tiger shark (Galeocerdo cuvier): dark stripes on the flanks, a broad head, opportunistic. 3) Whale shark (Rhincodon typus): the largest fish (up to 12m), a plankton filter feeder, white spots. 4) Hammerhead shark (Sphyrna mokarran): a T-shaped head (cephalofoil) that broadens vision and smell; a specialist hunter of rays. 5) Blue shark (Prionace glauca): a slender indigo-blue body, oceanic and a great migrator, long pectoral fins. — Identifying sharks trains scientific observation. Brazil has 88 species on its coast. The white shark is the most famous (the movie Jaws). The tiger shark is more dangerous to humans. The whale shark is a gentle giant. The hammerhead is unique for its shape. The bull shark is in Brazilian rivers (the Amazon). Knowing the species helps in conservation - 1/3 are threatened by overfishing. At camporees with a marine theme, identification workshops fascinate young people. Aquariums (AquaRio, Cetáceos do Cabo Frio) allow some to be seen live.

6. What is the importance of the Ampulla of Lorenzini?

   Answer: The Ampullae of Lorenzini are sensory organs unique to sharks (and rays) located on the head, forming a network of pores connected to tubes filled with gel. They detect extremely weak electromagnetic fields (down to 1 microvolt/cm) emitted by living beings: heartbeats, muscle contractions, brain activity. — Discovered by Stefano Lorenzini in 1678. These organs are so sensitive that they detect even the Earth (a magnetic sense). That is why sharks hunt in absolute darkness. Unlike the eyes (limited in murky water), the ampullae always work. Scientists study them to inspire technology (ultra-sensitive sensors). At camporees with a marine theme, laboratory demonstrations fascinate young people. It is an example of extraordinary biological design - an Adventist argument for divine intelligent creation.

7. What is the smallest and what is the largest shark that exists?

   Answer: Smallest: the dwarf lanternshark (Etmopterus perryi), at only 17-21cm in adult length (it fits in the palm of the hand), lives in deep waters of the Caribbean and has bioluminescent photophores. Largest: the whale shark (Rhincodon typus), up to 12-18m long and 19-21 tons, lives in tropical oceanic waters, is a plankton filter feeder and totally harmless to humans. — The diversity of sizes among sharks is impressive. The dwarf shark can hide in a hand; the whale shark is bigger than a bus. The whale shark is the largest living fish (non-mammal) on the planet. It is gentle and friendly - divers swim with them in the Galápagos, Maldives, Belize. Dwarf sharks are rare and little studied (they live at 200-500m depth). At camporees with a marine theme, illustrations with a human scale fascinate. Brazil has records of the whale shark in Fernando de Noronha.

8. Identify the main morphological structures of a shark through a diagram (which can be made by the Pathfinder or by the instructor).

   Answer: Head: snout (rostrum), eyes (with a protective nictitating membrane in some species), nostrils, mouth with teeth in rows, ampullae of Lorenzini. Trunk: 5-7 gill slits, spiracle (in some species). Fins: pectorals (lateral, provide support), pelvics (ventral; in males they form the claspers), dorsal (the iconic one), second dorsal (in some species), anal and the caudal fin (tail, the main propulsion structure, often heterocercal with a larger upper lobe). The skin is covered by dermal denticles (placoid scales) and the lateral line runs along the flank detecting vibrations. — Diagramming a shark trains comparative anatomy. Each structure has a specific function: the rostrum aids hydrodynamics, the spiracle breathes while stationary, the heterocercal fin provides propulsion, the placoid scales reduce friction (it inspired research into coatings for airplanes and submarines). The lateral line detects water pressure. At camporees with marine biology, a diagram with labels identifies knowledge. A colored diagram facilitates memorization. Each species has subtle variations that help with quick visual identification.

9. Visit an aquarium, observe cartilaginous fish and make a report on what you learned.

   Answer: Research aquariums (AquaRio in RJ, the São Paulo Aquarium, AquaMundo) with cartilaginous fish. Schedule in advance (school/club gets a discount). Bring a notebook and camera. At the aquarium, observe: the species present, behavior (continuous movement, feeding), interaction with the public, tank conditions (size, salinity, temperature). — Visits to aquariums are educational and fascinating. AquaRio in Rio is the largest in South America, with several sharks and rays. Live observation enriches theoretical learning. A notebook allows you to note details. A report consolidates knowledge. At camporees, a visit can be part of the program. Aquariums also have educational lectures. Conservation is a central theme - many cartilaginous species are at risk. Investing time in marine education generates lasting environmental awareness in young people.