Egg attributes and hatchling mass as predictors of hatchling growth on a Nile crocodile (Crocodylus niloticus) farm

Abstract

Rapid growth of Nile crocodile (Crocodylus niloticus) hatchlings on farms shortens the time to slaughter for skins, thus reducing costs and improving farm efficiency. The aims with the project were to assess the utility of various egg attributes (length, width, volume, mass and density) as predictors of hatchling mass (HMinitial) for 269 eggs from 15 clutches and to assess these egg attributes, HMinitial and egg productivity as predictors of the mass of the hatchlings 68–75 days after hatching (HMend). Hatchlings heavier than 61,5 g were individually marked and assigned to five pens according to HMinitial until the HMend of 129 hatchlings was determined. Strong and meaningful positive, linear relationships existed between HMinitial and all egg attributes except egg density, where the relationship was strong and negative (P < 0,001). HMend varied widely across as well as within clutches. It is most compatible with the data that HMinitial (P = 0,08) and egg productivity (P = 0,02) have meaningful negative relationships with HMend when all five pens are included in the model. Considering pens separately, the direction of the relationship between HMinitial and HMend was negative for three pens and neutral for two. The direction of the relationship between egg productivity and HMend was negative for four pens and positive for one. The models that each included one predictor as well as pen only explained 8–14% of the variation in HMend, suggesting that factors other than those studied largely affected growth.

Nylkrokodilbroeilinge (Crocodylus niloticus-broeilinge) wat vinniger groei op plase kan vroeër geslag word vir hulle velle, wat koste verminder en plaasdoeltreffendheid verhoog. Die projek se doel was om die nut van verskeie eierattribute (lengte, wydte, volume, massa en digtheid) as voorspellers van broeilingmassa (BMbegin) vir 269 eiers van 15 broeisels te bepaal, en om hierdie eierattribute, BMbegin en eierproduktiwiteit as voorspellers van die massa van die broeilinge 68–75 dae ná uitbroeiing (BMeinde) te beoordeel. Broeilinge swaarder as 61,5 g is individueel gemerk en volgens BMbegin aan vyf hokke toegewys, totdat die BMeinde van 129 broeilinge bepaal is. Sterk, betekenisvolle, positiewe, lineêre verbande bestaan tussen BMbegin en al die eierattribute behalwe eierdigtheid, waar die verband sterk en negatief was (P < 0,001). BMeinde het baie tussen en binne broeisels gevarieer. Dit is die beste versoenbaar met die data dat BMbegin (P = 0,08) en eierproduktiwiteit (P = 0,02) betekenisvolle negatiewe verbande met BMeinde het wanneer al vyf hokke by die model ingesluit is. Vir hokke wat afsonderlik beoordeel is, was die rigting van die verband tussen BMbegin en BMeinde negatief vir drie hokke en neutraal vir twee. Die rigting van die verband tussen eierproduktiwiteit en BMeinde was negatief vir vier hokke en positief vir een. Die modelle wat elk slegs een voorspeller en hok as koveranderlike ingesluit het, verklaar 8–14% van die variansie in BMeinde, wat aandui dat ander faktore as dié wat bestudeer is groei grootliks beïnvloed.