Biology of the acid‐tolerant fish species Umbra pygmaea (De Kay, 1842)

Abstract

In The Netherlands, the mudminnow Umbra pygmaea mainly occurs in water bodies with a pH ranging from 3–5 to 4–0, an alkalinity less than 0.1 meq 1−1 and a calcium content below 100 μmol 1−1. The abundance of mudminnows is inversely related to the pH and the presence of predatory fish species. Experimental studies show that If. pygmaea is extremely acid‐tolerant. Exposure to media with pH values ranging from 4.0 to 7.0 did not cause mortality or significant changes in blood plasma osmolarity and haematocrit. At pH 3.0 no mortality was recorded although a strong decrease in the plasma osmolarity was observed. Exposure to pH 2.8 and calcium concentrations of 100 or 500 μ mol 1−1 for 10 days caused 70% and 40% mortality respectively. The growth, reproduction and feeding of mudminnows are described. Age‐growth and length‐age relationships were calculated. Gonadal development started between September and January. The highest Gonado Somatic Index was recorded in spring. Spawning occurred from April to May. Fecundity of a sample of females was assessed. Nematocera provided the main item of diet of U. pygmaea; the microfauna ingested was dominated by Cladocera. The adaptations of mudminnows to acid environments are discussed.

Prolactin cell activity and sodium balance in the acid-tolerant mudminnow Umbra pygmaea in acid and neutral water

“…In contrast to other teleosts, which are unable to repro duce in water of p H < 5, mudminnows suc cessfully reproduce even at p H 3.5 (Dederen et al, 1986). The present data show that the unusual acid tolerance of mudmin nows is also reflected by the p H depen dency of prolactin secretion.…”

“…A survey of recently acidified freshwater lakes and bogs in the Netherlands has re vealed that in water below p H 5 only one species is able to survive: the East-American m udm innow (Dederen et al, 1986;Leuven and Oyen, 1987). It was introduced in Europe some 70 years ago and at present it frequently occurs in high densities in acid bog lakes at a p H as low as 3.1.…”

“…Since the main function of prolactin is the control of the branchial permeability to water and ions, in particular sodium (Hirano, 1986; W e n d e laar , we have inter preted the increased prolactin cell activity in acid water as an appropriate endocrine response for maintaining water and ion bal ance in acid water (Wendelaar Bonga et al, 1987;Flik et al, 1989). W e have evidence that prolactin is also involved in the accli mation to acid water of eels (Wendelaar Bonga and Balm, 1989).A survey of recently acidified freshwater lakes and bogs in the Netherlands has re vealed that in water below p H 5 only one species is able to survive: the East-American m udm innow (Dederen et al, 1986;Leuven and Oyen, 1987). It was introduced in Europe some 70 years ago and at present it frequently occurs in high densities in acid bog lakes at a p H as low as 3.1.…”

Umbra pygmaea, an acid-tolerant fish

“…0 , and a C a : ' co n cen tratio n o f less than lOOjiimol l " 1. T he species has even been found at a C a :+ co n ce n tra tion as low as 15 p m o \ 1 _1 [2]. T he low est pH level at which the fish has been observed under n atu ral conditions is 3.2.…”

“…Its original area o f distribution is in the eastern U SA . T oday it is w idespread in the south-eastern part o f the N eth er lands and in the province o f L im burg in Belgium, where it is particularly a b u n dant in acidified soft-w ater ecosystem s with a low pH , such as m o o rlan d pools (" v en n en " ), and usually the only fish species [1,2]. It can be found as well in circum neutral w aters but there, probably due to predation by large fish, Quantities are low.…”