Horned nerites

[hotweldfire]

http://www.planetinverts.com/horned_nerite_snail.html

Anyone keep these? I put 5 in my 12l office nano and they've done nothing. Were active for the first couple of days and for the last few days they've just been lying on their sides not moving.

Assumed they were dead and went to pull them out but when I pick them up they move again. Have dropped an algae wafer in amongst them and they haven't touched it. My assassin hasn't gone near them.

Is this normal? Are they in some kind of hibernation mode? There's at least a bit of algae to be eaten in the tank (which is why I bought the bloody things).

 

[JonE]

I've got a Zebra Nerite who is always on the move although when I first added him to the tank he was pretty inactive so maybe they just take a few days to get comfortable in their new home, he also managed to survive for a day out of the water after one of his escape attempts.

I've got one in an 8 litre tank and have never seen any algae on the glass, so your tank should be spotless in no time. They can starve to death if not supplemented with additional food though.

Where did you get yours from?

Cheers

Jon

 

[frothhelmet]

In my experience nerties cannot be supplemented with any food but algae on hard surfaces, they just ignore it. If you dont have enough of that or if you water is too soft and acid they will wither away and die. Your nerites behaviour is worrying Sajit. Let us know how it goes though...

 

[hotweldfire]

Shown absolutely no interest in an algae wafer dropped right on top of them. In fact my gouramis have eaten that instead (eventually). Still no movement and what looks like a crack in one of the shells so does not look good.

Gerard, what PH do you keep yours in? Is it both PH and hardness that matter or just hardness? TDS is between 200-250.

 

[frothhelmet]

Ph >7, Kh >5. Anything less and they wont like it. If you are little bit under they can tolerate it, but go more than a few decimal points and their shells will start to seriously corrode. I am having that problem on a tank at the moment with Ph 6.7 and Kh 3. I killed two nerites in there in about 6 weeks because the water bore a hole in their shells in that time.

 

[hotweldfire]

Thanks. Have you kept them in a low PH/high TDS tank? The reason I ask is that I got them from ADC who say they keep them in all their planted tanks. Most of those (if not all) will have injected co2 therefore PH likely to be under 7.

So I was wondering if it might actually just be water softness. Then I found this paper:

Journal of Freshwater Ecology
Volume 4, Issue 3, 1988
Effects of Acid Water on Shells, Embryos, and Juvenile Survival of Planorbella trivolvis (Gastropoda: Pulmonata): A Laboratory Study
R. Douglas Hunter

ABSTRACT
Adults of the freshwater pulmonate snail Planorbella trivolvis were maintained in aquaria at four pH levels of approximately 4.9, 5.9, 6.8 and 7.8. Adult mortality was moderate over 82 days (10–32%) and not related to the magnitude of pH reduction. Decrease in both shell calcium per unit tissue dry weight and shell calcium per unit maximum shell diameter were significantly related to both time of exposure and pH level. Both measures were significantly reduced after 53 days of exposure to acid water such that for mean Ca mg-1, pH 4.9=5.9 < 6.8 < 7.8 and for mean Ca mm-1, pH 4.9=5.9 < 6.8=7.8. Empty (ashed) shells without a periostracum lost CaCO3 about 4.6 times faster than did shells of live snails with periostracum intact.

Fecundity per snail did not differ greatly from one pH treatment to another although at pH 4.9 the embryos developed slowly and showed a high incidence (38.5%) of abnormality compared to embryos reared at pH 7.8 (4.8% abnormality). Juvenile survival at pH 5.1 was poor with 100% mortality by day 43. At pH 6.6 and 7.5, 9 (=4.1%) and 15 (=8.9%) individuals respectively were alive at day 93, some of which were functional adults laying eggs.

These experiments demonstrate that under laboratory conditions acidified natural water (pH 4.9–5.1) causes measurable snail shell erosion in adults, as well as embryonic abnormalities and increased juvenile mortality. Extrapolation to natural populations under stress due to acidification suggests that adult shell erosion, although unlikely to be a direct cause of death, provides an indicator of stress. A more serious threat to snail populations may be recruitment failure due to mortality of eggs and juveniles.

But don't have full text access so don't know if they controlled for water hardness. Also found this one

The effect of calcium and pH on Florida apple snail, Pomacea paludosa (Gastropoda: Ampullariidae), shell growth and crush weight
Nancy H. Glass1 and Philip C. Darby1

Abstract Pomacea (Ampullariidae) snails, commonly referred to as apple snails, serve as prey for many freshwater-dependent predators, and some species are highly invasive. Identifying limits to apple snail distribution and abundance are pertinent to understanding their ecology. Calcium (Ca2+) availability and pH generally influences freshwater snail populations, yet scant data exist for Pomacea snails. We measured 6-week change in shell length (?SL) in P. paludosa in two laboratory experiments with varying Ca2+ and pH levels. ?SL was significantly higher in =28 mg Ca2+/l compared with treatments =14 mg/l. Snails from populations living in low Ca2+/pH waters did not appear genetically predisposed at growing faster in these conditions. Smallest ?SL was in snails treated with 3.6 mg Ca2+/l and pH < 6.5 water; these snails had signs of shell erosion. Shell crush weights (CWs) were lowest for snails grown in the lowest Ca2+/pH treatment. Smaller shells and lower CWs have implications for predation vulnerability and reproductive success. Our results are consistent with reports associating relatively low snail densities with relatively low Ca2+/pH waters, and they are consistent with the geographic distribution of P. paludosa as related to the underlying water chemistry as influenced by geology.

But again, there isn't an experimental manipulation to tease the two factors out. No doubt harder waters are higher in PH but I can control the two factors somewhat independently so would be good to know what the mechanism of shell erosion is. In fact in the discussion they say

Distinguishing between the effects of calcium concentration and pH on shell calcium levels could potentially be done experimentally, but in natural systems, where we find apple snails, low pH and low calcium occur simultaneously

 

[dw1305]

Hi all,
I don't think it will matter whether it is lack of calcium or low pH, they will both have the same effect. If you had soft water, but with a pH above pH7, and fed the snails a calcium rich diet, they may be all right, but as soon as you add CO2 (to depress the pH) the carbonate ~ CO2 equilibrium would mean that shell erosion occurs.

I have had the same problem with Assassin Snails (Clea (Anetome) helena), even though the pH is usually just above pH7 the water was too soft for them, some tanks I can't keep Ramshorns in and even my MTS have eroded shell spirals.

All these Nerite snails are from salt(s) rich alkaline habitats (adults are euryhaline, veliger larvae marine and planktonic), and I would suspect they all have a fairly limited life span away from fairly hard, high conductivity water.

cheers Darrel

 

[hotweldfire]

Thanks. I have a similar problem with assassins in my main tank - they end up with blunted ends to their shells eventually. Unfortunately the pond snails they're meant to be eating seem to be a bit harder. Nerites look well and truly done for I'm afraid.