Bristlenose bristles

[Silurus]

Yan, HY, 2009. A histochemical study on the snout tentacles and snout skin of bristlenose catfish Ancistrus triradiatus. Journal of Fish Biology 75: 845–861.

Abstract

Histological sections of the tentacles of Ancistrus triradiatus revealed that they contain many goblet cells with granule-like sections distributed along the edge of the tentacles (mean 302 cells mm−1). Various histochemical methods were used to characterize the contents of the goblet cells. The results indicated that the contents were periodic acid-Schiff (PAS) positive, glycogen negative and no sulphated mucins could be found. The contents of the goblet cells were acid mucins and O-acetylated sialomucins which had high energy content. The snout skin of the male also contained goblet cells with higher density (mean 755 cells mm−1) than that of the tentacles. Snout skin of female A. triradiatus, on the contrary, did not contain any goblet cells. Instead, many minute spines could be found. Based on the acid mucins and O-acetylated sialomucins secretions of goblet cells which are of high nutritional values, it is hypothesized that snout tentacle secretions are used to provide nutrients to fish larvae when they are under paternal care.

[Richard B]

Very interesting indeed HH - thanks for posting

[Mike_Noren]

I don't buy their final speculation. I've never seen ancistrus larvae eating the mucus off their dads tentacles.

[Jon]

I don't see why it couldn't be possible, although, there is no correlation that I am aware of between bristle surface area of a species and fry yolk sac size or time in the cave. Furthermore, fry do not appear to leave the care of a male in a more developed state than other similar ancistrinae.

Also, it is worth considering and contrasting the life histories of young fish in those species which altogether lack or have little bristleage with our standard run of the mill species.

I certainly agree that the bristles are very likely to have some role in fry rearing- it would not be metabolically favorable for these fish to produce such amounts of mucins apparently. Immunologically speaking, one might also consider the use of these mucins in pathogen removal.

[Shane]

I certainly agree that the bristles are very likely to have some role in fry rearing

I tend to agree with the theory that they mimic moving fry and attract females who are led (by the males tentacles) to believe that he is already a successful father and thus worth mating with.

I think most of us have spawned and reared too many spp of Ancistrus to put any stock in this. Besides, fry and even eggs, taken from the father mature just as quickly as any fry left with the father. I can say this since I can never seem to actually catch and remove all the fry.

-Shane

[Jon]

The female selective theory (although it could very likely be a part of the big picture) wouldn't explain the mucus covering the processes. Why not just evolve processes that don't leak precious metabolic calories?

Theoretically speaking, fry, while still sacbound, are not feeding necessarily on the mucus--rather, the mucus is more likely a last meal for the fry once the sacs have been absorbed, and are ready for release. Fry artificially reared from eggs SHOULD grow just as fast because the aquarist provides his brood with nutrient packed prepared foods consistently, just as the male would.

[Jon]

Just a thought---did they test variances in bristle biology between rearing males and nonrearing males?

[MatsP]

Just a thought---did they test variances in bristle biology between rearing males and nonrearing males?

Given that they worked on dead specimens, I think it's pretty hard to tell.

--
Mats

[apistomaster]

I don't see why it couldn't be possible, although, there is no correlation that I am aware of between bristle surface area of a species and fry yolk sac size or time in the cave. Furthermore, fry do not appear to leave the care of a male in a more developed state than other similar ancistrinae.

Also, it is worth considering and contrasting the life histories of young fish in those species which altogether lack or have little bristleage with our standard run of the mill species.

I certainly agree that the bristles are very likely to have some role in fry rearing- it would not be metabolically favorable for these fish to produce such amounts of mucins apparently. Immunologically speaking, one might also consider the use of these mucins in pathogen removal.

I lean towards the last possibility you raised, Jon.
The bristle secretions may provide increased protection of the eggs and larvae from attack by bacteria and fungus.
But I think it is secondary to the role heavy bristle growth plays in mate selection. I think female Ancistrus preferentially mate with the males with the most well developed bristles. I had a trio of large albino Ancistrus cf.cirrhosus and both females would spawn consecutively with the male in the same day resulting in some large releases of fry, usually about 200 at a time.
It is notable that only males develop the truly impressive bristle growth even among the Ancistrus species where the females have some bristle development. It seems very much like the peacock males which have put so much into a conspicuous feature that makes them more vulnerable to predation but are preferred by the females. Sexual selection for exaggerated secondary sexual characteristics is a known driver in the evolution of unusual physical features in males of many species..

[Suckermouth]

I've been looking at Sabaj et al. 1999 (larval mimicry hypothesis) so this comes coincidentally at the right time for me.

Some people are arguing about whether the larval mimicry or the larval feeding hypothesis is the best explanation, however they are not mutually exclusive. It's not just the tentacles that have goblet cells, the snout shows goblet cells as well, and in fact in higher densities! It's possible that males in other genera also have these cells as they are not specific to the tentacles. Lasiancistrus comes as the obvious next step to study considering its close relationship and the presence of tentacules.

Theoretically speaking, fry, while still sacbound, are not feeding necessarily on the mucus--rather, the mucus is more likely a last meal for the fry once the sacs have been absorbed, and are ready for release. Fry artificially reared from eggs SHOULD grow just as fast because the aquarist provides his brood with nutrient packed prepared foods consistently, just as the male would.

Indeed. This study has a possible explanation to a question I was thinking about, and that's what larvae feed upon while they are in the cavity. Presumably the young are feeding on something. Certainly, if we removed fry for a few days and didn't feed them anything right after they absorbed their yolk sac, they would likely die. When the fish fry finally absorb the yolk sac and have to switch to solid foods is an extremely crucial time, and this occurs in the nest, so something makes that switch easier.

Just a thought---did they test variances in bristle biology between rearing males and nonrearing males?

All specimens were captured during the spawning season, so at the very least they are all in a "reproductive stage".
EDIT: I take that back, they cite evidence the goblet cells are around in non-reproductive fish, just not from this study.

Still, an excellent question. The hypothesis this paper proposes is analogous to milk production in mammals, and mammals pretty much only produce milk when they've had the hormonal triggers from pregnancy (if I'm not mistaken?). Obviously a different mechanism would trigger this in bristlenose males. Spending all that energy all the time doesn't seem like a good idea as Jon pointed out, especially as Ancistrus do not get to eat while they are in the cave.

Another question is to test the difference between adults and juveniles. Do juveniles have these cells? Do juvenile males have undeveloped goblet cells?

EDIT: Their discussion section puts out a lot more than the abstract. They talk about Discus (saying that it's hard to compare since we know so little about secretions from either), they talk about the possibility of anti-microbial function for the mucus, and the possibility that it's used as a chemical signal.

PS. Mats, is this discussion getting split off?

[apistomaster]

I believe I have noticed that sometimes L134 fry stay inside the cave slightly longer than is absolutely necessary and those broods that do emerge later are weaker than those that emerge at a more optimal time. I see two types of fry. Those that are quite vigorous and full bodied which have nearly 100% survival and then there are the come lately's which are thin and weak with much higher mortality rates. Males appear to exercise a good deal of control over when the fry are released.

[Borbi]

Hi,

just for completion:

The abstract is now available here and for those luck enough to have access to this journal, the full article can be downloaded here

Enjoy!

Cheers, Sandor

[Jools]

I'd be more inclined that if any mucus is adding value to the young fry, then it's rubbed off on the cave walls and then utilised. As others have said, I've never seen "fry in the bristles".

Jools

[Richard B]

i have seen occasional fry in the male's bristles (whilst in the spawning cave) but i do not think there was any other purpose to this other than concealment/seclusion & this is only a few of many & due to immediate proximity. I suspect if there was some nutrition available, the majority of the fry would attempt to gain it as opposed to an odd few. Fry of varying broods all seem to react the same when purpose-fed prepared food enters the tank, so it follows if food was vailable from a different source they would surely ALL act the same?

[bronzefry]

Could the chemicals in the bristles bring about an odor that the fry recognize? I often see the fry following the father long after leaving the cave. I've even seen juveniles going in and out of the cave when he's fanning the next brood. The female can't go in, but the juveniles can. Just thinking.
Amanda

[Jools]

The other thing that bothers me about this is that there are a whole load of other genera that spawn in caves. Why do only

Ancistrus

have tentacles?

Jools

[apistomaster]

The other thing that bothers me about this is that there are a whole load of other genera that spawn in caves. Why do only

Ancistrus

have tentacles?

Jools

Hey Jools,

That is why I think Ancistrus males' bristles have more to do with sexual selection than feeding adaptations.

[bronzefry]

The other thing that bothers me about this is that there are a whole load of other genera that spawn in caves. Why do only

Ancistrus

have tentacles?

Jools

Wicked good question.....some Ancistrus sp. have more bristles than others, too. What about the one that actually lives in the cave? Does that one breed in a cave in a cave and have bristles?
Amanda

[Janne]

In large males with a heavy growth of tentacles you can observe another thing too, when no eggs or fry in the cave the tentacles are soft and hanging down from the head, when there are fry in the cave the tentacles are stiff and upright... if I would impress on a female I would want to show I am stiff ;)

My own thought about the tentacles on Ancistrus species is more that they are used in the care of the offspring's, I don't think the fry are feeding from them... I have never seen that anyway. Females will probably be attracted of males with large and heavy growth of tentacles, that is a sign that this male will take good care of their offspring's.

Janne

[Suckermouth]

The other thing that bothers me about this is that there are a whole load of other genera that spawn in caves. Why do only

Ancistrus

have tentacles?

Jools

Wicked good question.....some Ancistrus sp. have more bristles than others, too. What about the one that actually lives in the cave? Does that one breed in a cave in a cave and have bristles?
Amanda

These questions are coincidentally answered in the new link that HH posted.

[Mike_Noren]

That is why I think Ancistrus males' bristles have more to do with sexual selection than feeding adaptations.

This is my opinion too. Many, perhaps most, "enigmatic" structures in animals, from human male beards to the brilliant colors of male Apistogramma, are due to sexual selection.

The one thing which suggests that the bristles are anything more than a fish visual equivalent of antlers is that they're full of goblet cells. Goblet cells are gland cells, but instead of larva-food I'd suspect they're producing pheromones - Ancistrus have very good sense of smell, and presumably males, being sedentary and cryptic, in nature need to lure females to their nests.

[apistomaster]

That is why I think Ancistrus males' bristles have more to do with sexual selection than feeding adaptations.

This is my opinion too. Many, perhaps most, "enigmatic" structures in animals, from human male beards to the brilliant colors of male Apistogramma, are due to sexual selection.

The one thing which suggests that the bristles are anything more than a fish visual equivalent of antlers is that they're full of goblet cells. Goblet cells are gland cells, but instead of larva-food I'd suspect they're producing pheromones - Ancistrus have very good sense of smell, and presumably males, being sedentary and cryptic, in nature need to lure females to their nests.

Hi Mike,
Sometimes we have very different takes on some subjects but I know how very accomplished you are in the art and science of aquatic animal culture such as your success with raising Amano Shrimp despite their complicated life cycle so you have always have had my utmost respect. It is pleasant to be in agreement and I think you raise an excellent point about the role that pheromones may play in the Ancistrus spp reproductive biology. It is rather rare for any unusually great sexual dimorphic features to only have a single function. It doesn't make sense to me that the goblet cells are of very much importance to the development of Ancistrus fry because those egg/larvae/fry which are incubated in isolation of the male's care do not seem to be any less healthy than those receiving the male's care.
Why Ancistrus males evolved their characteristic bristles and other plecos did not is impossible to know but these goblet cells are present in the noses of others genera lacking bristles and so it seems to me that pheromones must be used to transmit a male plecos' breeding status and is probably a universal among all the pleco genera. The males all seem to "set up shop" in caves and must await a willing partner in order to breed. Only pheromones can exert the necessary response from a female in search of a mate. Unlike peacocks displaying in the open, the Ancistrus and others have to chemically communicate their breeding status and their "cryptic" locations, regardless of water clarity.

[Suckermouth]

The author of this study obviously came upon this study trying to figure out why bristlenoses have bristles. However, personally this paper is not a complete, or maybe even relevant, answer to this question. At this point I think the finding of goblet cells is entirely irrelevant to the phenomenon of bristle growth in bristlenose males. This is because goblet cells are not only found on the normal snout skin, but on the snout skin they are actually found in higher densities than on the bristles! It is interesting, however, that these goblet cells are sexually dimorphic and only found in males. So, considering other male loricariids obviously have snout skin, it is not unreasonable to believe that other male loricariids without bristles also have goblet cells. But there's no evidence that anyone has looked for and found goblet cells in other loricariids; if that were the case, I'm sure it would've been mentioned in this paper.

[Jon]

Aren't the snouts of most ancstrines plated? That would assume that spongy tissue would not be present. If not for feeding, then it would seem the answer would be much more straightforward--the naked, unscuted tissue lining the rostral processes simply require some sort of barrier against pathogens, not unlike the glycoprotein slime coat found on all fishes.

[Shane]

Why Ancistrus males evolved their characteristic bristles and other plecos did not is impossible to know

Just using your statement to make a general point Larry.

Bristles are unique to Ancistrus, but changes to the rostrums of the males of various loricarid species are a fairly common trait for the family. During the spawning season male Chaetostoma experience a large swelling of the soft rostrum tissues giving them that "bulldog" look that earned them their common name. This has been noted among some spp of Lasiancistrus as well. Some Loicariinae grow odontodes on the rostrum (i.e. Farlowella vittata and Neblinichthys) as oppossed to those loricariids that grow extended cheek odontodes.

So no other genus currently described has bristles, but changes to male loricariid's rostrums during the spawning period are well documented for several genera.

-Shane

[Jon]

If you go by phylogeny, in less derived genera, such as lasiancistrus, the rostral tentacles are associated with odontodal growth, which, assuming this was a trait present in linkage species, was lost in later (i.e. ancistrus) species. Therefore, it is plausible to say that rostral odontodes are in some sense an analog of "bristles".

[Borbi]

Hi,

Therefore, it is plausible to say that rostral odontodes are in some sense an analog of "bristles".

Or, to extend that one (didn´t come up with that myself, just don´t remember where I read it):
you can just as well assume that the bristles developed from odontodes in that the odontodes are covered with some skin, which, later in the development, "detaches" from the odontode itself, forming a more or less stand-alone fleshy/skinny attachement that can then further evolve to the bristles we see today.
In that sence, Ancistrus spp. are simply the most evolved ones regarding this characteristic.

Cheers, Sandor

[Suckermouth]

Aren't the snouts of most ancstrines plated? That would assume that spongy tissue would not be present. If not for feeding, then it would seem the answer would be much more straightforward--the naked, unscuted tissue lining the rostral processes simply require some sort of barrier against pathogens, not unlike the glycoprotein slime coat found on all fishes.

The snouts of most ancistrines are plated, as I believe Ancistrus are diagnosed by having unplated snout margins. Apparently females have a more restricted unplated snout area compared to males. But despite Ancistrus females having unplated areas on the snout, they do not show goblet cells at all. If the naked, unplated region needed more protection, then wouldn't you expect goblet cells to be present in females as well? To be fair, the sampled region on the snout of females was between the nares, which I believe is a plated area in both males and females. On the males, the snout skin was sampled at the base of the tentacles, which may mean it was not necessarily on the snout between the nares.

Hi,

Therefore, it is plausible to say that rostral odontodes are in some sense an analog of "bristles".

Or, to extend that one (didn´t come up with that myself, just don´t remember where I read it):
you can just as well assume that the bristles developed from odontodes in that the odontodes are covered with some skin, which, later in the development, "detaches" from the odontode itself, forming a more or less stand-alone fleshy/skinny attachement that can then further evolve to the bristles we see today.
In that sence, Ancistrus spp. are simply the most evolved ones regarding this characteristic.

Cheers, Sandor

That's clearly right out of Sabaj et al. 1999, if you were wondering where you read it.

[Jon]

"Or, to extend that one (didn´t come up with that myself, just don´t remember where I read it):
you can just as well assume that the bristles developed from odontodes in that the odontodes are covered with some skin, which, later in the development, "detaches" from the odontode itself, forming a more or less stand-alone fleshy/skinny attachement that can then further evolve to the bristles we see today.
In that sence, Ancistrus spp. are simply the most evolved ones regarding this characteristic."

indeed. that's what I was inferring, hence why i referred to them as most derived.