Leuresthes tenuis

On the way to spawning grounds

The Grunion ( Leuresthes tenuis ) is a maximum of 20 cm long Atherinopside ( neuweltlicher Ährenfisch ), which is thus known to be spawning is coordinated with moon phases and carried out " on land ".

Description

It is the Grunion a silvery, very elongated ( thin ) fish of the Californian Pacific coast (he is only south of the Monterey Bay before ). The back and a ribbon along the sides are gray-green or bluish. The fish lives in 0-18 meters depth always coastal and near surface sociable plankton, possibly small juvenile fish.

Fins formula: D1 IV -VII, D2 I/8-10, AI/20-24, P 12-15, VI / 5, C 17

The two dorsal fins are quite far back, the first is small, its rays are thin and flexible. The small ventral fins are slightly behind the end of the pectoral fins. The anal fin is as long as both dorsal fins along with their distance. The caudal fin is bilobed ( the lobes often dark). The almost pencil -like, but flexible fish has 47-50 vertebrae and 6 Branchiostegalia. The first gill arch carries in top 23-29 Branchiospinen, down only 5-7. The eyes are large. The mouth is small and practically toothless, the upper jaw ( the premaxilla paired ) is increased more when the mouth opening (similar to parrots), but is not vorstreckbar, the lower jaw is short. The hull is covered with small cycloid scales (approx. 60-70 along the side lines - of which there are two each: a dorsal and a lateral, but both of them do not reach the tail fin - probably in connection with the grave activity ). The body is slightly flattened laterally, but the head is flattened above ( depress ), forehead ( dark) and pine are therefore quite broad. The skin is slippery ( Name: Greek: leurόs "smooth", esthēs " robe ").

Behavior

There are few creatures whose rhythm is so clearly connected with the lunar cycle (eg Palolowurm, the red mangrove crab ( Pseudosesarma moeshi ) ). Eggs are laid in the spring and summer (February to August) a few days after a new moon (or full moon ) tide as high up on sandy beaches ( where, for example to accommodate even horseshoe crabs (Limulus ) or sea turtles lay their eggs; see nor the capelin ( Mallotus villosus ) ). The fish meander about the scope of accrual of waves still short out and cause by violent movements (especially the tail) that as many eggs buried in the sand ( and thereby from the female slinging male fertilizes ) will. The behavior has the advantage that marine predators can not reach the spawning (but eg isopods, crabs, birds, beetles, even ground squirrels ) and the sand above the water line is usually well ventilated. The fry hatch 10-14 days later at the next high tide ( the hatching is triggered by waves that move the sand, but can optionally also be two weeks apart), are recognized by the waves and live it neustisch - nektisch.

A female can be eight years old and spawn up to four times per season ( per 1600 to about 4000 eggs). Sexual maturity occurs at about 10 cm in length, so sometimes even in fish of age 1 . The males are slightly smaller than females, which can be embraced by several milk formers spawning sometimes. The spawning game out of the water takes a half to several minutes.

The eggs are about 2 mm in size ( spherical ), without attachments (such as not often at Siluriformes ) and contain from one to over a hundred yellowish oil balls. You need to temperature and salinity variations be very tolerant ( develop at 10-28 ° C - but not in pure fresh water).

Endangering

The Grunion is a popular fish whose spawning behavior annually attracts onlookers. Since he is obviously not very common ( Further details are still unclear), he is protected ( now also locally in Baja California) since 1927 in California, to a certain degree - for example, he may only be taken by hand. However, this does not prevent the Grunion ends as by-catch in fishing nets. Its spawning beaches are z.T. under protection ( what environmental toxins from agriculture does not discourage ), the spawning can be excavated only for educational purposes, etc. Commercial fishing was due to low density and size never rewarding the Grunion but is considered palatable. Archaeological otolith finds that Grunions the spawning period represented a popular food already among the Indians. Of course, they are an important link in the food chain (eg as food for gulls, seals, dolphins and predatory fish ).

Relative

On the east coast of Baja California lives the very similar type Leuresthes Sardina ( Jenkins & Evermann, 1889), which is up to 25 cm long and spawns during the day. The separation of the two (now good ) species probably occurred in Neogene. Several types of Atherinopsidae are the Grunion eidonomisch and ecologically quite similar, such as top and jacksmelt ( Atherinopsis ). Very similar is the " wrong Grunion " Colpichthys regis Jenkins & Evermann, 1889. The real " smelts " on the other hand, although ( smelts ( Osmeridae ) ) live are similar but Stomiatii, that is, with the Protacanthopterygii related (to which u a salmon fish are ) - they have no prickly (front ) back, but an adipose fin; Mallotus villosus and Hypomesus eg.