C

Cartilaginous

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A Blacktip Reef Shark (Carcharhinus melanopterus) has a fully cartilaginous skeleton (photo credit: David Clode).

If you’ve ever eaten a fish fillet, you’ve probably had the ‘pleasure’ of picking out fish bones from your meal.  While most fish are, indeed, bony (superclass: Osteichthyes), certain lineages of fish have cartilaginous skeletons, meaning that their skeletal structure is composed of cartilage, like a human ear or nose, rather than bone.  Elasmobranchs (sharks, skates, and rays) and chimera (class: Chondrichthyes) have always had cartilaginous skeletons.

 

Atlantic Sturgeon | NOAA Fisheries

Atlantic Sturgeon (Acipenser oxyrinchus oxyrinchus) have secondarily derived cartilaginous skeletons (photo credit: NOAA).

Chondrosteans (sturgeon and paddlefish; subclass: Chondrostei) are another group of cartilaginous fish – but with a more complex evolutionary history.  The ancestors of sturgeon and paddlefish had fully ossified, bony skeletons (they are members of Osteichthyes) but they have evolved to have secondarily derived cartilagenous skeletons (i.e., cartilage ➡ bone ➡ cartilage).  They do still retain some bony elements – scutes which are modified bony scales.

 

 

Cetí (Español – English)

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Ceti is the term for post-larvae of the Puerto Rican native S. plumieri (photo credit: Catherine Goodson).

Las comunidades locales puertorriqueñas se refieren al pes nativo postlarva, S. plumieri, como cetí. Las especies de peces de agua dulce puertorriqueña como “dajao,” “gauvina,” y “olivo,” (nombre común del cetí en su fase adulta) son anfidromas. La historia de vida de estos peces incluyen una fase de aqua dulce y marina. En particular, los olivos adultos viven y se reproducen en las partes altas de los ríos, mientras que las larvas derivan río abajo hasta llegar al mar en donde se convierten en post larvas conocidas como cetí (Erdman 1961).Como resultado, grandes bancos de cetí migran río arriba durante el último cuarto de fase de la luna de cadaciclo lunar, de junio a enero en Puerto Rico (Engman et al. 2017).

Durante la migración río arriba, el cetí se enfrenta a altas Corrientes, depredadores, y perturbaciones naturales y antropogénicas. Por esta razón, tiene un disco de succión ventral que le ayuda a sobrevivir  durante el fase adulta y la fase de cetí. El Olivo (nombre común de S. plumieri)  utiliza el disco de succión ventral para escalar cascadas y otras estructuras, como represas (Keith 2003). Por esta razon, también se les llama chupa piedra. El Olivo  hembra puede crecer hasta 103 mm de largo, mientras que los masculinos pueden identificarse por su color azul irredescente. Si van de visita a Puerto Rico, generalmente pueden encontrar al olivo debajo de las rocas en los ríos o millones de cetí que migran río arriba.

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Cetí is a term used by local communities in Puerto Rico to refer to native fish species, S. plumieri, during their post-larvae life history. Puerto Rican native freshwater fish, such as mountain mullet, bigmouth sleeper, and sirajo goby, are amphidromous. Their life histories include both fresh and salt water phases; adults reside and spawn in pools and eddies of the upper parts of rivers, while the larvae drift downstream into the ocean, where they reside until they develop into post-larvae, or “cetí” (Erdman 1961). Schools of cetí locate a source of freshwater and proceed to migrate up stream during the last quarter moon phase of each lunar cycle, from June to January in the Caribbean region (Engmanet al. 2017).

During their migration, cetí, as well as other post-larvae native fish species, compete against high currents, predators, natural disturbances and anthropogenic factors. A trait that aids their survival during their cetí and adult phases is their ventral sucking discs which they use to climb the wet surfaces of waterfalls, rocks and any man-made structure with any type of flow (Keith 2003). For this reason, they have been given the nickname “chupapiedra”, meaning rock sucker. Female sirajo (S. plumieri) can grow up to 163 mm, while males can be easily identified by their blue-ish iridescent colors. If you happen to be in Puerto Rico, you can usually find Sirajo gobies underneath rocks in the rivers or millions of post-larvae migrating up the river mouths.

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References:

Engman, A. C., Kwak, T. J., & Fischer, J. R. (2017). Recruitment phenology and pelagic larval duration in Caribbean amphidromous fishes. Freshwater Science, 36(4), 851-865.

Erdman, D. S. (1961). Notes on the biology of the gobiid fish Sicydiumplumieri in Puerto Rico. Bulletin of Marine Science of the Gulf and Caribbean, 11(1), 448–456.

Erdman, D. S. (1986). The Green Stream Goby, Sicydiumplumieri, in Puerto Rico. Tropical Fish Hobbyist, 34(1), 70–75.

Keith, P. 2003. Biology and ecology of amphidromous Gobiidae of the Indo-Pacific and Caribbean region. Journal of Fish Biology, 63 (1), 831-847.

Creel Survey

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A creel survey in action (photo credit: AFS).

Guest post: Logan Neu, University of Minnesota Twin Cities

A creel survey (also known as an angler survey) is a type of in-person survey performed by resource managers where an interviewer asks an angler questions about their fishing experience including questions such as the duration of the trip, how many fish they caught, and if they were satisfied with their experience.  The interviewer may also ask about the angler’s thoughts about a future management decision. Additionally, harvested fish are counted and measured.

Creel surveys are performed to gain insight about recreational angling perceptions, efforts, and harvests in order to inform future decision making.  Creel surveys are a valuable tool for fisheries managers to use in understanding the systems they manage and how the public interacts with them.

Culvert

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Three perched culverts (photo credit: USFWS).

A culvert is essentially a tunnel to pass flowing water, typically a small stream, under a man-made structure, usually a road.  Depending on the size, placement, and design of a culvert, the impacts to a stream channel vary.  These impacts, in turn, can affect fish habitat and fish migration.

Culverts are frequently barriers to fish movement.  If culverts are perched, where the outlet is higher than the elevation of the downstream water, fish are required to leap up into the culvert (if they are able) to continue moving upstream.  Often, culverts are not installed to be perched from the outset, but the situation is caused by erosion at the outlet of the culvert from high flows which scour the channel bed.  This type of culvert creates a downstream pool, changes the flow velocity and habitat type, and, consequently, can alter the fish community as well.

Local, state, and federal managers often work to replace or retrofit culverts that have significant ramifications for fish passage.  The U.S. Fish & Wildlife Service’s National Fish Passage Program is one example.

Countershading

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Guest post by Emily Argo

Countershading, originally described in the late 1800s, is when one side of an animal is dark and the other is light, serving as a form of camouflage. In fish, such as the Atlantic Bluefin Tuna (Thunnus thynnus) pictured, this typically means the ventral side (bottom) is light and the dorsal side (top) is dark. This is useful for fish because the dark dorsal side helps them blend in the with substrate or deeper water below if they are being viewed from above. Then, the lighter dorsal side helps fish blend in with the water (and light backdrop of the sky) above them if you are looking at the from below. Countershading is seen in fish species in coastal and open ocean habitats.

Atlantic Bluefin Tuna are one of many pelagic species that exhibit countershading.

However, some species, such as the Nile catfish (Synodontis batensoda), exhibit reverse countershading where the ventral side is dark and the dorsal side is light. The Nile catfish feeds while swimming upside down in the water column and the reverse countershading helps it camouflage.

While evidence of the mechanisms that drive countershading are lacking, studies suggest that there is an adaptive advantage to countershading in aquatic habitats where the scattering of light through the water column remains relatively uniform throughout the day compared to terrestrial environments (Ruxton et al. 2004).

Can you think of other animals that exhibit countershading?

Reference:

Ruxton, Graeme D., Michael P. Speed, David J. Kelly, What, if anything, is the adaptive function of countershading?, Animal Behaviour, Volume 68, Issue 3, September 2004, Pages 445-451, ISSN 0003-3472, http://dx.doi.org/10.1016/j.anbehav.2003.12.009.
(http://www.sciencedirect.com/science/article/pii/S0003347204001794)

Chondrichthyes

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Chimaeras are a predominately deep sea branch of elasmobranchs with most found deeper than 200m (NOAA).

Chimaeras are a predominately deep sea branch of chondrichthyes with most found deeper than 200m (NOAA).

Chondrichthyes are a taxonomic class of cartilaginous fishes that encompass sharks and rays (elasmobranchs) and chimaera.  Though there are exceptions, in general, Chondrichthyes have exposed gills, no swim bladder, internal fertilization, and placoid denticles.  These characteristics differentiate them from the more evolutionarily derived branch of fishes, bony fish (Osteichthyes).

Catadromous

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Eels have a unique larval form, leptocephali, which can utilize marine currents to travel long distances.

Eels have a unique larval form, leptocephali, which can utilize marine currents to travel long distances.

A catadromous fish hatches and spawns in salt water but spends most of its life in fresh water.  Catadromous life cycles are much less common than anadromous life cycles.  American and European Eels (Anguilla rostrate and A. anguilla, respectively) are among the more famous fish that utilize this unusual migration pattern.  They have a highly specialized larvae, leptocephali, which resemble a transparent leaf.  Their specialized shape allows leptocephali to ride marine currents to the continental shelf using relatively low amounts of energy.  In coastal waters, they metamorphose into glass eels.  As they continue to grow and start developing pigmentation, they enter the yellow eel phase.  Yellow eels migrate into estuaries and onto fresh water where they will remain until they reach sexual maturity as a silver eel and return out to sea to spawn.

For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!

Caudal peduncle

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The caudal peduncle is the narrow region of a fish's body anterior of the caudal fin.

The caudal peduncle is the narrow region of a fish’s body anterior of the caudal fin

The caudal peduncle is the tapered region behind the dorsal and anal fins where the caudal fin attaches to the body.  The depth of the caudal peduncle, which is measured at its narrowest point, gives some indication of the power of a fish and the speed at which it can swim.  For example, ambush predators, like barracudas or gars, have a caudal peduncle that is not much narrower than their torpedo-shaped bodies.  They can lie-in-wait and then give a few powerful thrusts of their tail to surprise a prey fish.  Other very fast swimming, powerful fish, like tunas and mackerels, have a very narrow caudal peduncle.  They can even have keels, like those on a boat, to help support and stabilize the caudal fin and make swimming far and fast more efficient.

A narrow caudal peduncle is common in fast, far-ranging fish

A narrow caudal peduncle is common in fast, far-ranging fish

Ctenoid scales

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Ctenoid scales are characterized by small teeth on their posterior margin

Ctenoid scales are characterized by small teeth on their posterior margin

Ctenoid scales are scales with comb-like edge found in higher order teleost fishes, such as perch and sunfish.  Cteni are the tiny teeth on the posterior margin of the scale.  Similar to cycloid scales, they are overlapping which allows for greater flexibility in movement than other types of scales such as ganoid scales.  The surface layer of the scale is comprised of calcium-based salts and the inner layer is predominately collagen.  As a fish grows, its scales grow, adding concentric layers, similar to tree rings.  For certain species, these rings can be counted to estimate the age of a fish.

Cycloid scales

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Cycloid scales are characterized by having a smooth margin

Cycloid scales are characterized by having a smooth outer margin

Cycloid scales are smooth-edged scales predominately found in lower order teleost fishes, such as salmon, carp and other soft fin rayed fish.  Similar to ctenoid scales, they are overlapping which allow for greater flexibility in movement than other types of scales such as ganoid scales.  The surface layer of the scale is comprised of calcium-based salts and the inner layer is predominately collagen.  As a fish grows, its scales grow, adding concentric layers, similar to tree rings.  For certain species, these rings can be counted to estimate the age of a fish.