Spawning seasons may vary considerably among populations of the same species. For example, in the North Atlantic, there is a spawning herring population at any time of the year.

The SPAWNING table therefore presents information on the spawning season, sex ratio, absolute and relative fecundity, fecundity-length relationship and daily spawning frequency of various stocks (populations) of the same species at various localities.

Country and Locality fields identify spawning locations, while the Spawning ground field refers to the habitat type where spawning occurs which may be: lacustrine; riverine; estuarine; coastal; shelf; oceanic.

The spawning Season states the months of the year when spawning takes place. The monthly percentage of mature females can be entered here. When ‘111’ is used here, this refers to months during which mature females were reported, but without indication of their relative abundance.

A graph can be generated to show the seasonality of reproduction in a given stock, and which is based either on percentages, or entries of ‘111’ values. In the latter case, the data are smoothed (over 3 months), which also generates approximate standard errors. Also, a composite graph can be generated which combines the data of several graphs into a single plot. When its standard errors are low, this indicates a similar seasonality of spawning for all stocks of the same species (see Fig. 45).

Fig. 45. Seasonality of spawning in Engraulis ringens off North/Central Peru.

The Temperature field gives the range of water temperature in degree Celsius at which spawning normally occurs, while the Sex ratio pertains to the average percentage of spawning females in a spawning stock. If a published % Sex ratio was given as a fraction (number of females/number of males), it was transformed using:

                                                  number of females
% Sex ratio =    ---------------------------------------------------- · 100
                                  number of females + number of males

Fecundity, defined as the number of eggs found in a ripe female, is often reported in the literature without indication of the corresponding body weight. While such information is less useful than relative fecundity (see below), we decided to nevertheless include it in this table. To accommodate cases where size information is available, we added fields allowing entry, for each fecundity record, of a range of body weights and lengths. Also, a choice field is provided to identify the type of length measurement used. The choices consist of: SL (Standard Length); FL (Fork Length), TL (Total Length), WD (Width of Disc, in rays), NG (not given in source) and OT (other length type).

The Relative fecundity is given where available and defined as the number of mature oocytes in a female divided by the total weight of that female.

The Fecundity-length relationship would be the most useful information but is rarely given in the literature. Still we have provided fields for entry of this information, as follows:

Size: consists of two fields referring to the smallest and largest fish considered when the fecundity-length relationship was derived. A choice field defines the type of length measurement used (see above);

n: pertains to the total number of specimens used for deriving the fecundity-length relationship;

a: refers to the multiplicative factor a of the fecundity-length relationship of the form F = aL^b, wherein F is the fecundity in number of eggs and L is the length in cm;

b: refers to the exponent of the fecundity-length relationship;

r: pertains to the correlation coefficient of the log-linear form of the fecundity-length relationship.

The Daily spawning frequency applies to batch spawners only, and gives the frequency of spawning per day (e.g., 0.5 means half of the females spawn every day, i.e., an individual female spawns every second day, see e.g., Hunter and Goldberg 1980; Hunter and Leong 1981; Pauly and Soriano 1987).

Additional information about spawning site and season is given in the Comment field.

The SPAWNING table contains over 2,800 records for more than 2,000 species. Many entries contain only the spawning season, but over 700 records also report sex ratio or fecundity.

The present coverage will expand and gradually assimilate the huge volume of available literature on spawning, especially on commercial species.

You get to the SPAWNING table by clicking on the Biology button in the SPECIES window, the Reproduction button in the BIOLOGY window, and the Spawning button in the following window.

In the Internet, you get to the SPAWNING table by clicking on the respective link in the ‘More information’ section of the ‘Species Summary’ page. You can create a list of species with available data by selecting the Spawning radio button in the ‘Information by Topic’ section of the ‘Search FishBase’ page.

Hunter, J.R. and S.R. Goldberg. 1980. Spawning incidence and batch fecundity in northern anchovy, Engraulis mordax. U.S. Fish. Bull. 77:641-652.

Hunter, J.R. and R. Leong. 1981. The spawning energetics of female northern anchovy, Engraulis mordax. U.S. Fish. Bull. 79:215-230.

Pauly, D. and M. Soriano. 1987. Monthly spawning stock and egg production of Peruvian anchoveta (Engraulis ringens), 1953 to 1982, p. 167-178. In D. Pauly and I. Tsukayama (eds.) The Peruvian anchoveta and its upwelling ecosystem: three decades of change. ICLARM Stud. Rev. 15, 351 p.