Wainwright Lab

University of California, Davis

Category: fish feeding

Some new videos, the Fingered Dragonet

It’s been a while since we had a new video to post, and this will be a quick one, but it is a pretty interesting fish. We recently got some new fish in the lab, including some dragonets from the family Callionymidae. These fish are mainly found in the Indo-West Pacific in tropical waters and are typically benthic. Some from the genus Synchiropus are found in the hobby industry, but are apparently tough to maintain because they feed on benthic invertebrates. We have two species in the lab currently and have started trying to film them. One, we have had some success with, the fingered dragonet (Dactylopus dactylopus). From the videos below you can see a couple of interesting features of this fish, one is that the first two fin rays of the ventral fins are modified for walking along the bottom. This is similar to Inimicus didactylus, which you can see in a few posts back, that has the first two pectoral fins rays modified for walking. The other unique feature of this fish is the way it feeds, which is pretty different than a lot of the videos we have posted, and the topic of Sarah’s (new grad student in the Wainwright lab) dissertation. It has some pretty unique jaw protrusion!

By any other name

We’ve had some great posts on Fishbase and fish eyes recently, thanks to Carl and Lars. Most of the lab is working on abstracts for SICB 2012, so let’s get back to some fish videos.

This week’s contender is Petenia splendida, a fish-eating cichlid from Central America. If you saw one of this in a fish store, it would probably be called a “red bay snook”. The name isn’t particularly accurate: the fish is rarely red, doesn’t live in a bay, and isn’t a snook.

What this fish does have, though, is an impressive set of jaws for capturing prey. Petenia splendida is an impressive piscivore (fish-eater) that has some of the most protrusible jaws of any cichlid.

Where do they get all those wonderful videos?

This blog is also posted on my personal blog.

I joined the Wainwright lab in October of last year. While I had experience with swimming fish, including high-speed video analyses, I had not done any filming of fish feeding. At the beginning of this year I got my first taste of obtaining high-speed videos of fish suction feeding. Since that time I have been amazed at the diversity of fish the lab studies (for example, check out the Inimicus didactylus video), the speed of the strikes, and kinematics during the strike; some of the little fish have quite a big gape to capture their prey. The data we are gathering is allowing us to get a glimpse of the patterns of diversity in the kinematics during suction feeding among various species of marine fish, as well as the potential morphological and mechanical correlates of that kinematic data.

Many of the videos that we obtain as a result of this research we upload to our Youtube channel to share with the public, usually the best videos, in focus and lateral. When we film we always try to get focused and lateral sequences for subsequent digitizations. These clear lateral videos allow us to digitize several landmarks on the fish during the strike sequence to get several kinematic variables such as maximum gape, time to pre capture, and ram speed to name a few. But we don’t just need clear lateral videos to showcase on Youtube; we mainly need clear videos to be able to track the landmarks throughout the sequence, and we need lateral videos to obtain accurate kinematics. For example, if the sequences are not clear, it may be harder to track a landmark and there may be more error because the points may drift. If the fish isn’t completely lateral, we may not be able to see all the points, or if the fish as at an angle (going into the third dimension, such as toward the back of the aquarium, which we don’t capture in the 2-dimensional video) the kinematic variables may not be accurate. So, there is a reason for us obtaining these clear lateral videos. However, we also recognize that some of these strike sequences are pretty amazing, so we share them on Youtube.

Lately, our videos (especially the Inermia vittata video you can see in a previous post) have attracted the attention of several science, news and tech blogs. Thank you to all that have posted our videos. However, obtaining these videos is not always easy work, something else that I have learned since being a part of the Wainwright lab. Obtaining these sequences can sometimes (and often) take lots of hours of filming, patience, and hard work. Much of this depends on the fish or the species. Some fish are very good performers, and obtaining several good sequences does not take long (for example the Histrio histrio you can in another previous post). Others require some training to get the fish use to the lights required to capture the sequences at 1000 frames per second. Furthermore, not every fish feeds perfectly lateral every time, or we have multiple individuals in the aquarium that all want food, and the fish themselves are not always perfect. In fact, there are plenty of instances when the predator will miss the prey. This itself is interesting; a former Wainwright Lab member Tim Higham has done some work on the accuracy of strikes, what makes a predator accurate and what can make them miss? Perhaps having a farther strike distance and faster strike velocity decreases accuracy, but to compensate, species have larger gapes to ingest a greater amount of water to increase chances of prey capture (e.g., Higham et al. 2007). We recently posted a video on our Youtube channel of some of these ‘outtakes.’ Again, it is not always easy to capture the clear lateral videos and it takes a lot of work, so this video highlights a ‘bad day at the office’.

Patrick Fuller on feeding duty, Tomomi Takada on camera duty during a typical filming session.

So how do we get all these wonderful videos? First, it is almost always a two person job (although Matt has filmed sticklebacks alone). One person feeds the fish, trying to get them in view of the camera, and striking laterally. This job is almost an art form in itself. You have to learn the behavior of the fish; are they sit and wait predators like the frogfish, fast strikers like the white-streaked grouper, or more active swimmers like Inermia vittata? Therefore, the person feeding has to be aware of the fish’s behavior to try and get good sequences. Challenges may also arise is there are multiple individuals.

Another view of a filming session

We want to ensure all fish eat and we want to get sequences from all individuals, so the person feeding has to keep track of the fish or target the various individuals. The other person involved in the process is the person responsible for tracking the prey and predator, focusing the camera and triggering the high-speed camera. This job is also not easy. It takes some skill to track and focus and quickly trigger the camera. We film at 1000 frames per second and many of the videos on Youtube are played back at 10 frames per second. So what do these strikes actually look like in real time, how much time does the person manning the camera have to respond? To demonstrate this we made a video of a full sequence captured during filming,  in real time and about 200ms of that sequence played back at 10 frames per second for comparison. The person on camera duty has 3 seconds to trigger. You can see from the video, the person responsible for this part of filming either has, or hopefully obtains quick reflexes!

Although our Youtube channel features some of the best sequences we capture, keep in my mind we always strive to get the best videos. And the next time you see one of our videos on Youtube or elsewhere remember that one video is probably the product of hours of work. I want to also note that many of these videos are the work of undergraduate assistants we have in the lab. Many of our Youtube ‘stars’ were captured by our undergraduates, their assistance has been greatly appreciated and many of these videos would not have been captured without them.

Inermia vittata: Camera Debut

Below is one of the first ever recorded high-speed video sequences of Inermia vittata, a zooplanktivore from the tropical western Atlantic.  We are using its first live appearance in the lab to see how the feeding kinematics of Inermia compare with that of other reef fishes.  Watch how far that upper jaw projects forward!

One common name for this fish is the bonnetmouth, named after the appearance of the protruded mouth.  Like other reef zooplanktivores, Inermia appears qualitatively to be specialized at picking prey from the water column.  As you can see in the video, the mouth reaches forward, closing the distance to the prey while preparing to pull the prey closer with suction.

The evolutionary relationship of Inermia to other species has been tricky to resolve because it is very similar in appearance and behavior to other zooplanktivores such as fusiliers (Lutjanidae).  However, molecular analysis shows Inermia to be nested within the grunts (Haemulidae), which typically feed on benthic invertebrates.  A look at the pictures below will show how much different Inermia appears from a typical grunt and how similar it looks to the distantly-related fusilier.

boga boga bonnetmouth boga

Our new star, Inermia vittata

Doubleline fusilier

A fusilier, nested within the snappers (Lutjanidae)

French grunt

A close relative of Inermia

Why does Inermia look so different from a typical grunt, and why does it look so similar to a distantly related species?  Perhaps the feeding mechanisms captured in these videos can help to resolve this evolutionary anomaly.

An optical illusion?

Zooplanktivory is one of the most distinct feeding niches in coral reef fish and many morphological traits have been interpreted as adaptations to feeding on plankton in the water column above the reef. One of these traditional hypotheses is that zooplanktivorous fish have larger eyes for sharper visual acuity. A larger eye usually has a longer focal length and thus is expected to produce a better-resolved image.

Peter and I tested this hypothesis with a data set on eye morphology of labrids (wrasses and parrot fishes):

Schmitz, L. & P.C. Wainwright (2011). Ecomorphology of the eyes and skull in zooplanktivorous labrid fishes. Coral Reefs, 30: 415-428. reprint.

Labrids are a species-rich clade of reef fish with enormous morphological and ecological diversity. We sampled a total of 21 species, with three independent origins of zooplanktivory: Clepticus parrae, the Creole Wrasse (photo: fishbase.org), Halichoeres pictus, the Rainbow Wrasse (photo: wetwebmedia.com), and Cirrhilabrus solorensis, the Red-eyed Fairy Wrasse (photo: fishbase.org).

To our surprise we failed to find any indication of larger eyes in zooplanktivores. We tried several methods, including phylogenetic residuals of eye diameter on body mass and evolutionary changes in eye size along branches leading to zooplanktivores, but zooplanktivorous labrids did not show any signs of having larger eyes than other trophic specialists. Instead, we suspect that the notion of large eyes in zooplanktivorous labrids is an optical illusion evoked by a size reduction of the anterior facial region, which makes the eye look bigger.

However, we did find other features interpreted as adaptations to zooplanktivory in labrids. Both Clepticus parrae and Halichoeres pictus have a large lens for given axial length of the eye, related to better visual acuity, a round pupil, possibly an adaptation to search a three-dimensional body of water for food, and longer gill rakers to help retain captured prey.

Our results are quite interesting in that they highlight the importance of many-to-one-mapping in form-function relations. There often is more than one possible pathway to perform a function. In labrids, increase in eye size to improve visual acuity apparently is not part of the evolutionary response. But, let’s see what we can find in other groups!

Is this fish crazy?

This post is cross-posted with my personal website’s Blog.

We recently got some new fish in the lab, Butis butis, commonly called the crazy fish or Duckbill Sleeper. This is a fresh water fish, originating from East Africa to Fiji and belongs to the Eliotridae. These fish get to a maximum size of about 15 cm total length, live in brackish mangrove swamps and estuaries, feeding on small fish and crustacean, and is commonly found in the hobby industry.

The question is, are these fish in fact crazy? These fish tend to be unique because they can be seen swimming, floating, and even eating upside down. This behavior has been noted in nature and in aquariums, where they will also be seen pressed up the glass. They tend to be ambush predators and are often found floating among plants, in any position. Having them in the lab, we have begun filming them and have been able to capture their feeding right-side up and upside down. What will be interesting to see is if the kinematics of their feeding differs between the orientations, as well as if one orientation is better than the other at eliciting successful strikes. In the meantime, enjoy the videos of these crazy fish feeding in the two orientations.

Upside down filmed at 1000 frames per second, played back at 10 frames per second.

Right-side up filmed at 1000 frames per second, played back at 10 frames per second.

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