Tag Archives: Fish

Bait Ball: Have You Ever Heard of It?

A bait ball is a spherical formation that a school of fish make when they are being threatened by larger predators, such as dolphins, sea lions, and bigger fish. This instinctual behavior is a defense mechanism so that fewer fish are exposed during this feeding frenzy. When a school of fish has no protection from rocks and crevices they must use their vast numbers to their advantage. Bait balls typically do not last longer than ten minutes due to the vast amount of energy it takes to make this tightly packed ball. It is typically a fishes last ditch defensive measure because it can draw the attention of other predators like birds and sharks.

Bait Ball marlin

mackerelEach fish coordinates with its neighbor through visual site and the use of their lateral line. The lateral line is an organ located along both sides of the fishes body. Noted by faint dots along their scale, this lateral line can sense subtle pressure changes in the water and help direct them instantaneously.

Here at Catalina Island you can see a bait ball almost everyday, in varying sizes and species. Here are the most common species of fish that make up bait balls around Catalina Island.

Bait Ball sea lion feeding

Pacific Sardine:

  • distinctive flashy quality
  • release air bubbles as they swim
  • freckles on back
  • greatest body width underneath pelvic fin

Northern Anchovy:

  • appear glittery or sparkly
  • random solitary fish open their mouths wide and flare their gill covers in order to feed
  • dark on back with no markings
  • jaw shifted farther back
  • elongated body that is straighter and thinner than sardines

Jack Mackerel:

  • often hover motionless as if they were frozen,
  • can mix in with other species of fish
  • lateral line bends down due to longer pectoral fin
  • back is blue green or brassy brown
  • symmetrical dorsal and anal fins







Video Content from Gretchen Beehler and Anthony Julien

The California Halibut Part 1

First, they wait, buried up to their eyes…  As soon as their prey is within reach…AMBUSHl!  TEETH! GOT EM. And guess what? Halibut can chase their food as well, even leaping out of the water to do so.. if it’s their favorite (anchovies)…  Who doesn’t love anchovies?!

california halibut

Paralichthys californicus, the California Halibut, is a large flatfish found in nearshore waters, though they can be found as deep as 600ft.  Full grown halibut can get up to 5ft and 72lbs. You may see more of them in shallow waters from February to September because this is when the adults migrate from the continental shelf to spawn.  Juveniles spend their days in shallow-water bays and estuaries, making them especially vulnerable to habitat destruction by human activities such as dredging and pollution. Let’s be careful, friends!

california halibut 1

Halibut, despite what you may think, are laterally flattened fish, as opposed to dorso-ventrally flattened.  One side of their body always faces up, and the other always faces down, with the halibut always swimming on its same side.  With both eyes on the top facing side of their body, halibut rely heavily on a visual ambush as a method for feeding. They may be hard to spot due to their ability to change their skin pattern and camouflage with sandy and rocky bottom terrain, but this helps them to ambush their prey by catching them off guard.  

california halibut 2These fish are most abundant from central California to Baja california, and tip the charts as far as “yum” factor.  In fact, California halibut is one of the most important commercially-fished species among all state-managed fisheries.  To learn more about halibut, like how its eyes migrate to one side of its face, look out for part two!


comic: http://talesofabsurdity.com/comic/today-in-fish-news/



Sheephead Transformation

Ever seen a fish cake before? This one might look a little unusual. It’s one of the most exciting fish to find on a snorkel (or as your birthday cake), called the California sheephead (Semicossyphus pulcher). Sheepheads can grow to be over thirty five pounds and a full three feet long. They can live over 30 years and they play an important role in marine ecosystems by eating sea urchins that might otherwise eat all the kelp.  However, their lifecycle is the reason why sheepheads often take the cake as most interesting fish. If you’re looking for a fish to satisfy your intellectual hunger, check out the California sheephead!

Sheepheads are all protogynous hermaphrodites, meaning they all start out female with the potential to morph into a male later on in life. When they hatch, juvenile sheepheads have bright red bodies with a white stripe across their body and black splotches on their fins. As they grow, the white stripe fades and the fins lose the black spots, becoming entirely red while their lower jaw turns white. A sheephead can have vivid colors like bright red or more subdued tones such as a pale pink. After growing from anywhere from six to twelve years, a sheephead can finally change into a male!

The change from male to female varies between individual fish. Usually a female can morph into a male when there are no other males living nearby (or not enough males) and she is the most dominant of the females in the area. Dominance can be established by big mouth competitions – two sheepheads will swim at each other while opening their mouths as wide as possible, sometimes even locking jaws. However, other factors can influence whether or not this change occurs, including where the sheephead lives, how large she is, how quickly she grows, when she matured, and the amount of fishing in the area. Sometimes, slower growing females will never change.  

If a female successfully starts morphing into a male, it’s no cakewalk. There are a couple changes she’ll experience. Her body colors adjust: her torso remains red but her caudal fin (tail fin) and head turn black, except for the chin. Talk about a five o’clock shadow! The fish also grows a large hump on the forehead. Finally, the sheephead’s reproductive organs change due to changing hormones. The ovaries reabsorb any eggs inside while transforming into testicular tissue. Then, the newly male sheephead can claim his own territory and begin life as a male!


Hamilton, Scott L., Jennifer E. Caselle, Julie D. Standish, Donna M. Schroeder, Milton S. Love, Jorge A. Rosales-Casian, Oscar Sosa-Nishizaki, 2007. Size-Selective Harvesting Alters Life Histories of a Temperate Sex-Changing Fish. Ecological Applications, 17(8), 2268-2280.

Loke-Smith, Kerri A., 2007. 15 California sheephead, Semicossyphus pulcher. Status of the Fisheries Report, 2011.

Love Milton.

Warner, Robert B., 1975. The Reproductive Biology of the Protogynous Hermaphrodite Pimelometopon pulchrum (Pisces: Labridae). Fishery Bulletin 73(2).

The Giant Sea Bass

Let me introduce you to the King of the Kelp forest, the Giant Sea Bass. This behemoth of a fish can grow up to nearly 7 and a half feet long, can weigh a whopping 560 pounds, and can live to the ripe old age of 75. These fish were, at one point, a prized catch by fishermen. Now, critically endangered, an encounter with a Sea Bass is a rare, exciting, and memorable event.

giant sea bass adult

These mega-fish begin their lives as tiny planktonic larvae, adrift in the ocean at the mercy of the currents. As they grow into juveniles the Giant Sea Bass is golden in color with distinct black spots. As they grow into maturity, which can take up to 10 years, they lose their bright coloration and turn gray. Their spots, while still visible, are less permanent.

Giant Sea Bass juvi

Adults are apex predators. Top of the food chain. As such, these fish are a keystone species. Without the Giant Sea Bass the kelp forest ecosystem in which they reside would be drastically changed. On a daily basis the sea bass feeds on a variety of critters that also find their home in the kelp—fish, rays, crustaceans, squid, and sometimes kelp itself. Generally slow swimmers, the sea bass seeks prey that lives on the bottom of the sea floor. Their caudal fin (tail fin) is built, however, for short bursts of speed if need be. Say if, perhaps, the Giant Sea Bass finds itself face to face with its one and only known natural predator: the Great White Shark.





Mola Mola Song

The Ocean Sunfish also known as the Mola Mola is perhaps the most strangely intriguing fish in ocean. Its appearance is more alien like than anything else though it isn’t from out of this world. The Mola Mola belongs to the class Osteicthyes that means bony fish. This differs from chondricthyes, which are fish that are made of cartilage like sharks or rays. The Mola Mola is particularly interesting fish. Though it is a bony fish that belongs in the order tetraodontiformes, which includes puffer fish and triggerfish, it lacks several structural features that are prominent on most of their fish cousins. The most glaring absence is the caudal fin (tail fin) and the presence of elongated dorsal and anal fins, which it uses to swim. They also lack a swim bladder, which is a special organ in bony fish that helps them maintain neutral buoyancy. Ocean Sunfish have buoyant skin to help them float which is very beneficial since Mola Mola have the potential to be large. They are the heaviest of all bony fish with some specimens recorded weighing over 5,000 pounds. To grow to such a size one would think that Mola would be carnivores with a high protein diet but instead they are pretty passive eaters that mainly eat jellies that they come across in the ocean. Some specimens have been found to have brittle stars and pieces of fish in their stomachs indicating that they may have a broader diet than previously thought.

mola mola flat

The Mola Mola is received the name Sunfish because their tendency to lay flat at the surface basking in sunlight. Historically they were thought to be planktonic and only go wherever the ocean currents would take them but Mola Mola are actually very strong swimmers that have the ability to dive to fairly deep depths. Sunfish have been observed swimming as deep as 600 meters. One theory that has yet to be proven is that Mola Mola bask at the surface to warm themselves up after extremely deep dives. They have also been known to swim beneath kelp rafts to let fish such as senoritas eat ecto-parasites that attach to their skin. On occasion they will even let birds like seagulls peck the parasites from their skin.

mola mola skin

Mola Mola are found in every ocean except the arctic but breeding grounds or seasons have not been determined. Mola Mola do however lay over 300,000,000 million eggs per individual. The sunfish lays more eggs than every other know vertebrate.

Mola Mola have very few predators. Sharks, Orcas, and Sea Lions have been known to prey on Mola Mola but do not do it habitually. Humans do not regularly fish for Mola and there isn’t a market for them in most parts of the world. Humans are however the biggest threat to Mola due to bycatch from commercial fishing operations around the world.

mola mola 2

Ichthyology 101

There are plenty of fish in the sea. Seriously, there are. There are over 30,000 different species of fish around the world and they all have similarities and differences that have been documented through careful study over time. The study of fish is called ichthyology and people have been practicing ichthyology for millennia. The earliest form of fish study was learning the most efficient way to catch them. Learning how they bred and where their breeding grounds were was invaluable information.


Nowadays we know more about fish than ancient peoples could have imagined. We have learned that some of the biggest fish in the ocean begin their lives as microscopic plankton. Some fish journey for thousands of miles to breed at the same breeding grounds they were born at but had never returned to since. Some fish change from male to female and vice versa. The list could go way on.

When it comes to specifying fish there are three basic categories to place them in. the categories are Osteichthyes, Chondrichthyes, and Agnatha.

The class Osteichthyes is contains what most would consider the classic type of fish. These fish have skeletons that are made out of calcified bones, they have fused jaws, contain a swim bladder, and an operculum that covers their gills. The majority of the 30,000+ Species of fish belong to this class.

Ichthyology 1

The second class of fish is Chondrichthyes. This class of fish is defined by their cartilaginous skeletons. The most recognizable members of this class are sharks but rays and skates are also members as well as other cartilaginous fish.

Ichthyology 3

The last class is Agnatha. This bizarre class of fish is defined not by what it has but rather what it doesn’t. The Agnathans lack jaws and only have two living members, the lampreys and hagfish.

Ichthyology 4

The study of fish is becoming more important every day with the growing human population. The increase in human population increases pressure on fish populations primarily the ones that are hunted for food. By fully understanding every aspect of a fish we can help insure that fish populations and Species will survive and potentially the human race as well.



Fishing Methods for a Sustainable Future

Raise your hand if you like eating fish! Many of you probably raised your hand as fish is something that tastes delicious and can be very healthy for you. But is the fish that you are eating harvested in a way that’s healthy for the ocean? It’s hard to know for sure. There are many commercial fisheries that gather fish in a sustainable way. However, there are fishing methods that are destructive to the environment and result in lots of bycatch and habitat destruction. Today we are going to talk about some common commercial fishing methods, some that are sustainable and some that are very disruptive to the marine environment.

First off let’s cover what bycatch is. Bycatch is the term for catching a species of marine animal that you were not intending to catch such as a seabird, turtle, shark, or dolphin. There is an estimated 160 to 170 billion pounds of wildlife pulled from the ocean each year. 63 billion of that is bycatch accounting for 40 percent of all wildlife pulled. The scariest part about this statistic is that it is by no means correct, there is no way to estimate the total bycatch numbers in the ocean because most goes undocumented.

Here are 5 major commercial fishing methods being implemented around the world today. We are going to cover them briefly as well as rate the sustainability score of each method 1 being not sustainable whatsoever to 5 being the most sustainable.

  • Gillnetting/ Driftnetting (1): Basically, a massive curtain of net that is suspended using floats or anchored using weights. The netting is essentially invisible so fish swim into the net and get their gills caught (hence the name). Gillnetting is incredibly successful, but also in terms of bycatch as it entangles dolphins, sharks, and sea turtles. The United Nations and many other countries have banned this approach.
  • Trawling (2): Think of a huge net being dragged behind a boat. The boat is hoping to catch large schools of fish within the net and tire them out forcing them into the back of the net. This practice can be done on the bottom of the ocean or in midwater. Bottom trawling for shellfish and flatfish is especially dangerous and results in massive habitat destruction and bycatch. Bottom trawling’s impact can be lessened by limiting trawling areas and midwater trawling by avoiding areas with lots of marine mammal and sea turtle traffic.
  • Longlining (2): Longline fishermen throw out a central line behind the boat that can go on for up to 50 miles. On this central line dangle thousands of smaller hooks that are left dangling in evenly spaced intervals. These hooks are meant to catch large open water fish like swordfish and tuna but as they are left out they attract other fish and birds that unfortunately don’t survive until the hooks are picked out of the water. If you took the 94 fisheries in the Gulf of Mexico and stretched their long lines out the total length would reach from Miami to London. This technique can be made better by sinking hooks deeper and using different hooks to limit bycatch.
  • Purse Seining (2): This huge net is used on schooling fish in the open ocean by surrounding the school, pulling the bottom of the net closed, and dragging it to the surface. This is more sustainable than others because certain schools are targeted and spotted and not randomly dragged about. However, bycatch is present through the sheer size of nets used and the number of fish caught in each haul.
  • Trolling (4): You have probably seen this one along coastlines where a boat has multiple lines being dragged behind a boat. This is a sustainable approach to open water fishing because soon after being caught, fish are brought to the boat and released without as much stress as other methods. This method has very low bycatch levels and is a sustainable approach!


All of these commercial fishing methods result in the bycatch of many important. ocean animals. Some methods I did not mention are target specific, meaning that you fish for exactly what you want and do not result in bycatch, such as cast netting, harpooning, spearfishing, rod and reel, and beach seining. All of these are essentially negating bycatch as you get exactly what you want without affecting the other aspects of the ecosystem.

fishing 1

If you want to help this issue of bycatch through commercial fishing take a look at the Monterey Bay Aquarium Seafood Watch website to find out which types of species are caught which ways. This can help you choose the right kinds of fish to eat! Or you can do it the old-fashioned way, grab a fishing rod or spear gun and get whatever fish you want…as long as you have a fishing license.



Seafood watch is a registered trademark of the Monterey Bay Aquarium Foundation


Rays vs. Skates

Snorkeling above the sandy bottoms of CIMI’s shores, you might spot a cute little ray shuffling along… or is it a skate? No wait, it is a ray! But it might be a skate. Maybe. These closely related cartilaginous fish can certainly be difficult to tell apart, but each has certain qualities that make it unique and distinguishable.

rays vs skates

Though both rays and skates have flattened bodies with which they can hide on the ocean floor, skates typically have fleshier tails with enlarged, thorny scales running along their backs for protection. Meanwhile, most rays have thinner tails barbed with one or two stinging spines that ward off potential predators. If you happen to see these guys moving about, you might observe that they swim differently too. Skates move by undulating their tails left and right, whereas rays flutter and flap their pectoral fins to get where they need to go.

Beyond the differences that you might notice at a glance, rays and skates have unique life cycles with disparate modes of reproduction. Skates are oviparous, which means that they reproduce by laying eggs. These eggs (or “mermaid purses” as they’re often called) are dark and flat with small projections that keep them anchored to marine substrate. Each egg is equipped with nutrients to keep the developing skates healthy for up to 12 weeks, at which point the pup will hatch and take on the big bad ocean. Rays, on the other hand, are viviparous, meaning that they give live birth to their pups. The gestational period (a.k.a. pregnancy) of some ray species can last over a year and once born, the juvenile rays usually separate from their mothers.

Ever Wonder What These Things Are?

The next time you find yourself face to face (or fin to fin) with a flat cartilaginous fish, remember these differences so that you can distinguish the tail-stinging, fin-flapping, birth-giving rays from those back-spiking, tail-swinging, egg-laying skates.




Do fish sleep?

Did you have the chance to go on a night snorkel while you were at CIMI? If so, you may have seen all kinds of fishes actively swimming around – even in those late hours of the night! You may have asked yourself, if they’re moving around with their eyes open during my day snorkel and my night snorkel… when do these animals sleep? Do they sleep at all?!

fish sleep

Credit: The Fisheries Blog

The question of sleep in fish is a complicated one. Generally, we associate sleep in mammals with three distinguishing factors: (1) closed eyes, (2) a circadian, or daily, period of rest, and (3) reduced activity in the neocortex, a special part of the brain that helps with sight and hearing. Fish, however, lack both eyelids and a neocortex! So the question of sleep is more about the fish’s behavior, and whether they exhibit this circadian period of reduced activity and responsiveness to stimuli. For most species of fish, this is the case! Many species like our favorite garibaldi, kelp bass, and blacksmith, rest at the bottom of their habitats at night with no detectable eye movement, lower respiratory rates, and slowed responses to stimuli. You can even see some sleeping in our tanks!

fish sleep 1

Credit: Phil Watson, shaaark.com

There are exceptions to this, however. Many researchers believe that pelagic species, ones that live in open ocean environments, continually swim in order to maintain ram ventilation of their gills and sustain breathing. These pelagic species include many types of sharks, tunas, bonitos, and mackerels.

fish sleep 3

What’s more, some shallow water species that do generally sleep may stop sleeping during certain periods of their life, like migrations or while caring for their young! Hey, sound familiar?

fish sleep 2

How Fish Use an Otolith on their Ocean Odyssey

Fish spend their entire lives swimming all over the ocean. But have you ever seen one trip or fall on the journey? A major reason why fish are not the klutzes of the ocean is due to the otolith that they posses.


Halibut otoliths (ThoseAlaskanGirls.blogspot.com)

The otolith of a fish is a hard, calcium carbonate structure that is located behind the brain of osteicthyes (bony fish). Due to the otolith bony fish are able to detect sound waves and gravitational forces that are present in the water. This in turn aids with their ability to hear and maintain balance while swimming all around the world.

Otolith 1

Otoliths help fish detect sound waves in the water (animal-store.ru)

Although all bony fish have an otolith, however it ranges in both size and shape depending on the species. There are also three different types of otolith that may aid a fish with their balance and hearing:

  1. The first of the otolith types is the Sagitta. This is the largest of the types and helps fish in their ability to hear by allowing them to convert sound waves into electrical signals that in turn allows them to detect any sound present in the water.
  2. Asteriscus, the second type of otolith, helps a fish detect sounds in the water as well.
  3. The final type of otolith, Lapillus, is how bony fish are able to detect not just sound waves, but gravitational forces as well.

Otolith 2

Otoliths help fish keep their balance (TheArgonauts.com)

Something else extremely awesome about the otolith of a bony fish is that it allows scientists to detect their age! Just like the rings of trees an otolith has growth rings present on it that allow scientists to estimate how old that fish may be. Not only that, but each individual ring is essentially its own unique fingerprint. This helps scientists examine the feeding habits and even migration patterns of each individual fish!

Otolith rings

Thin section of a rockfish otolith (University of Texas)

Although the otolith is extremely useful for our bony fish friends, not all fish possess one. When it comes to our cartilaginous fish friends (sharks, rays, and skates) they must rely on different adaptations present in their bodies to aid with balance and hearing due to their lack on an otolith.

Written By: Alex Feltes






We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit www.cimi.org for additional information. Happy Reading!