The present autecological investigations on the spined loach, Cobitis taenia Linnaeus, 1758, focus on the reproductive biology as well as on the ecology of early life stages. The spined loach is a small, bottom dwelling freshwater fish belonging to the loach family (Cobitidae). Adults are specialised inhabitants of sandy bottoms, according the reproductive biology only a description of spawning is present, that describes an embracement of the female by the male. Data on the ecology of early life stages are lacking. The species is considered threatened in Germany as well as in many other European countries and on European level.
Under standardised conditions in laboratory aquaria female spined loach spawned in intervals of three days to three weeks. Each of the up to 18 clutches per year contained 62-1156 eggs (median 278). Spawning behaviour was in agreement with literature reports, no communication between females or between males was observed. Care for the offspring was reduced to a pronounced choice of dense vegetation as spawning substrate. This preference was present also in the field.
Early ontogenetic stages (egg to larvae) displayed typical optimum-response curves with comparably broad ranges of tolerance regarding salinity (vital range 0.01 – 6.00 ‰), temperature (range 12 – 31° C, optimum range 18 – 26° C) and oxygen concentration (lower lethal limit 2 mg O2/l, no significant effect above 3 mg O2/l). Early stages of spined loach express several morphological adaptations for an enhanced oxygen uptake (external gill filaments, enlargement and strong vascularisation of fins, finfold and yolk sack). Values of temperature and oxygen concentration in the field as well as the salinity values in the known distribution area were in close accordance to the optimum values found in the experiments. From the present results a special adaptation of the spined loach to comparably warm habitats with potentially low oxygen concentration was postulated.
When faced to several potential predators, early ontogenetic stages of spined loach showed neither escape or burrowing behaviour nor chemical or morphological defence. The survival of the early stages seems to depend on indirect mechanisms of defence.
Spontaneous mobility of the free embryos and larvae was small (0.3 – 1.0 cm/h), but increased dramatically when the animals were placed into a gradient of light. From the second day after hatch, with completion of eye pigmentation, the embryos displayed a negative phototaxis. With beginning of exogenous feeding the reaction shifted towards a positive phototaxis.
The life history, the inhabited microhabitats and ontogenetic niche shifts during early ontogeny of spined loach were constructed from the present results. Spined loach pass at least four phases of different ecology: I) development of egg and embryo until eye pigmentation in the dense vegetation; II) further embryonic development until beginning of exogenous feeding at the bottom beneath the dense vegetation; III) the larval period in the transition area of vegetation and open sandy bottom; IV) the juvenile period at fine and comparably open sandy bottom.
In the light of these findings shallow, open areas with low water movements can extend the definition of suited water for spined loach. These areas should warm up considerable and contain subareas with dense vegetation as well as subareas of fine sandy bottom. Conservation measures for spined loach should focus on preservation of waters with such fine scaled structural diversity.